Mistaken for Cheating

Similar to Mistaken for Gay, this is when a character is wrongly accused of cheating on his spouse or girlfriend because of a series of misinterpreted clues. Usually these clues look very suspicious (a bra left in his apartment, lipstick on his collar, a romantic note) and the real story is hard to believe. The wrongly accused may protest "Wait! I Can Explain!" or "It's Not What It Looks Like!" If the spouse or girlfriend is another major character, the conflict will be resolved; if the love interest is a Girl of the Week, she may storm off, thus ending the relationship.

Shows aimed at kids also have a version where it's the kids who wrongly suspect that one of their parents is cheating on the other.

One notable property of this trope is that it can be used on shows that, because of their genre or their scrutiny by Moral Guardians, could never use a plot that involved actual adultery. But you can get some of the same benefits from a story where a character wrongly believes that adultery is going on.

See also Mistaken for Index. Often part of an Idiot Plot; and can result in Poor Communication Kills, at least figuratively. May be resolved with The Grovel.

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 * Here it's played for laughs. Quite well, in fact.
 * For what it's worth, that's a (well-done) version of a 30-year-old urban legend.

Anime & Manga
"Himeji: This bra isn't your size, Yoshi-kun..."
 * Forms the basis of some of the plots in Ah My Goddess, when Belldandy suspects Keiichi is cheating on her. In the end it always turns out to be a Not What It Looks Like moment, or in Hild's cases, manipulating him and the goddesses in order to try to steal him away.
 * Happens a lot in Baka and Test to the two main guys, Akihisa Yoshii and Yuuji Sakamoto. In one hilarious incident, Shouko demands access to Yuuji's cellphone, and after she starts to strip him in order to find it, he gives it to her. She then finds a text written to him by Akihisa, asking if Yuuji would let him stay over at his place that night. She immediately assumes that they're in some kind of illicit relationship. Later the main characters go to his house for a study session (and to see why he didn't want to go home), and the two girls who like Akihisa immediately also start questioning him as to why there's women-related clothing and items in his apartment (which turns out to be his sister Akira's stuff, who's visiting him to make sure he's not goofing off).

"Girl 1#: Don't just stand there, Akane.
 * Surprisingly, Pokémon featured an instance of this in one episode -- May's father Norman and the local Nurse Joy were actually setting up a fireworks display celebrating Norman and Caroline's anniversary.
 * Happens multiple times to Ranma from Ranma 1/2, almost always in a way that goes far beyond mere lipstick on his collar. A few examples:
 * Caught in bed with a girl snuggled up to him, both of them asleep (the girl slipped into his bed while he was asleep).
 * Caught with a girl attached to him like a barnacle while both of them are naked (she sneaked after him into the furo as a cat and glomped him).
 * Caught shoving a girl down onto a table while grabbing one of her breasts and shouting "Now give it up!" (No, seriously, it really isn't what it looks like.)
 * Ironically, the one time he did want to be Mistaken for Cheating in order to get out of a commitment, he used a very literal Lipstick Mark (which he applied himself in female form) and it was casually brushed off by the girl in question.
 * The entire student body always jumps to the conclusion that Ranma is cheating on Akane.

Akane: What do you mean?

Girl 2#: Ranma is making moves on another woman again."

"Yusuke: Wait, Keiko! It's not what you think!
 * Thanks to a misinterpreted conversation eavesdrop in a chapter of The Tyrant Falls in Love, Morinaga comes to believe that Souichi is having a sexual relationship with Isogai. (The truth is far more embarrassing for Souichi: he was blackmailed by Isogai, who discovered the relationship between him and Morinaga, into singing the Doraemon theme song on karaoke nights at Isogai's place.) One part that does not follow this trope is the discovery of hickeys on Souichi's neck which Morinaga takes as solid proof, forgetting that he made them himself several days ago.
 * One Planetes episode begins with Lavie seeing Fee talking to Director Dolf; as he's on a balcony a good distance away, he can't heard a word of it and assumes they have ulterior motives. (They're actually discussing Fee's possible promotion.) When he tells the rest of Debris Secton about this, they come to the en masse conclusion she's cheating on her husband. This lingers until Ai finally just asks Fee about it. Jump Cut to Lavie taking a roundhouse kick in the chest for having started the rumor.
 * It didn't help that, previous to their work at Technora, Fee and Dolf were coworkers at a small firm, and thus are still friendly to each other in private.
 * In the manga version of Shaman King, Anna mistakes Yoh's new Oracle Bell as a pager that a girl gave him. It doesn't help his case that he had a long black hair on his clothes from Silva. In the game Power of Spirits, this is taken further when Meril, a girl Yoh had never met until this point, walks in and hugs him.
 * Happens in Seto no Hanayome when a series of events results in Lunar's father walking in on Nagasumi rubbing Lunar's ass. Everyone immediately assumes that he was cheating on San, including San herself. Despite the fact that this exact circumstance (mermaid gets wet, reverts to mermaid form, forcing Nagasumi to dry them off, only for them to turn human at the worst possible time) has happened to her.
 * Kyou Kara Maou: Wolfram is always accusing Yuuri of cheating and Yuuri never is.
 * Lampshaded in Yu Yu Hakusho, when Keiko misunderstands Yusuke's relationship with Botan, who is just a friend and a partner to the spirit dectective.

Keiko: How do you know what I'm thinking?

Yusuke: Because I know what it looks like!"


 * In Bakuman｡, Akito Takagi, seeking ideas on how to write female characters, meets fellow mangaka Yuriko "Ko Aoki" Aoki, but keeps the meetings secret from his girlfriend Kaya Miyoshi out of fear that she would get jealous over him turning elsewhere for advice. While there, he meets his former classmate and academic rival, Aiko Iwase, who gives him a copy of her book with a letter inside. Miyoshi then discovers the letter and becomes quite upset until the misunderstanding is cleared a few chapters later.
 * In the chibi "Tenipuri Family" episodes of the Prince Of Tennis anime, Inui is Mistaken for Cheating by Oishi (his wife) when Ryoma tries on his mother's lipstick and later uses one of Inui's shirts to wipe it off, leaving a Lipstick Mark.
 * Shi from Wandering Son mistakes Yuki for cheating with one of the protagonists, Takatsuki, in his first appearance; she's touching him rather suggestively on the face. The creepy part is that Yuki is in her mid-twenties at youngest, and Takatsuki was only eleven.. And a girl dressed as a boy, though neither Shi nor Yuki knew that (though Yuki seemed to have guessed).

Comicbooks

 * Mary Jane Watson's Aunt Anna once tried to get her to face the "truth" about Peter Parker's apparent infidelity, what with all his sneaking around at odd hours and missing committments with the flimsiest of excuses; this aggravated MJ enough to evoke a Sarcastic Confession: her husband was really Spider-Man.
 * A story in Shock SuspenStories #11 called "Three's a Crowd" had a paranoid man believing his wife was cheating on him with his brother and he murders them both.
 * Another story in the same comic was based around a man being extremely possessive of his much younger Trophy Wife. When she mentions a new male friend, the husband believes she is having an affair, and shoots her friend dead from a distance.
 * Superman had to deal with this in one story when Lois discovered a pair of Lana Lang's panties in their bed which the jealous Lana had planted during her last visit.
 * Jimmy Olsen has been known to be Disguised in Drag on more than one occasion. After one such example, though, Jimmy got read the riot act by Lucy Lane. Turns out Lucy found in his apartment the purse, perfume and jewelry that were part of the masquerade lying around his apartment, but she thought he was dating someone else behind her back.

Fan Fiction

 * In this fanfic, Lex is caught "cheating" on Clark Kent with Superman, mixing Mistaken for Cheating with Two Person Love Triangle in a PR disaster.
 * In Through a Diamond Sky, this kicks off the plot. Jordan thinks that Kevin's secretive behavior, bizarre references, and long periods of no accountability are proof she's married a cheater - again. (He's husband #2). While it's true that he's up to a lot of very strange things in Cyberspace, an affair isn't one of them.
 * In the Ben 10 Hero High: Sphinx Academy, Ren suspects this of Ben when she has noticed him hanging out with Julie several times, though more often than not he is getting help from Julie to get a gift for Ren for their upcoming anniversary. It doesn't help that Susan is the one encouraging the idea.

Films -- Animated

 * In The Incredibles, Helen finds one of Mirage's hairs on Bob's suit, then overhears the second half of Bob and Mirage's phone conversation. Even after discovering that her husband had secretly resumed superhero work, she finds him hugging Mirage.

Films -- Live-Action
"Frank Drebin: I swear, it's another woman!"
 * In Enchanted, Giselle, just coming out of the shower, trips and falls on top of Robert, who had tried to catch her. Then walks in Nancy...
 * Subverted in the Brazilian movie Meu Tio Matou um Cara ('My Uncle Killed a Guy') Éder finds a series of pictures that seem to indicate that his girlfriend Soraya cheated on him with Kid. She then explains to him that he looked at the pictures in the wrong order, and they tell the story of a perfectly innocent afternoon. Later, the protagonist Duca mentions to a friend that the sun's position in the sky don't match Soraya's story, and Eder was right after all.
 * At the end of Pirates of the Caribbean 2: Dead Man's Chest,
 * It's not nearly that simple, and as evidenced by the dialogue, the three were intended as a love triangle throughout most of the second and third movies.
 * Jack seems to have a thing for women who are already taken. Davy would have skipped the debt and killed him out right if he knew Jack  And if Jack ever believed for a second he had a chance against the film's only One True Pairing, he'd better keep those delusions for his Pearl and that jar of dirt.
 * Humorously inverted in The Naked Gun 33 1/3. Lt. Frank Drebin first tells his wife Jane he's seeing another woman as a cover story, then Jane misinterprets a clue that leads her to believe that Frank really is cheating on her, so she forgives him.


 * In Knocked Up, Pete is making up lies about work and sneaking out of the house so that he can go see his.
 * In Transformers: Revenge of the Fallen, Mikaela walks in on Sam apparently sharing a passionate moment with an attractive co-ed, and storms off in a huff as Sam desperately protests that it's Not What It Looks Like.
 * Inverted in The Shop Around the Corner: Mr. Matuschek knows his wife is cheating with one of his employees and comes to the conclusion that it is Mr. Kralik.
 * Occurs in Who Framed Roger Rabbit, when Jessica Rabbit visits Eddie Valiant to ask for his help with her case. On the line "I'm desperate Mr. Valiant, can't you see how much I need you," Valiant's girlfriend walks in. It doesn't help that his pants are down as well.
 * That Lady in Ermine had this, due to Executive Meddling. Angelina's husband thinks she slept with the Colonel to make him leave (it was the ghost of her ancestor in a dream, convincing him to leave).
 * An odd example in Top Hat. Dale has confused Jerry for her friend's husband, Horace. Jerry loves Dale and Dale is convinced he's trying to have an affair with her.

Literature

 * Subverted in Reginald Hill's Dalziel and Pascoe novel Death's Jest Book, in which Sgt. Wield gets into a paternal relationship with a rent boy that sure makes it look like he's cheating on his partner--even Dalziel thinks so--except that he isn't. Ironically, Wield's partner is the one who hangs a lampshade on the situation by pointing out that he has complete faith in Wield's motives.
 * Turns up regularly in the works of PG Wodehouse, often on the most hair-triggered and flimsy of pretexts.
 * Happens with in the Night Huntress books when she's told that "the vampire" is in a bedroom with another woman. Becomes a Crowning Moment of Funny when she furiously pounds on the door only to find she's got the wrong vampire.
 * Used tragically in Needful Things. Fiancees Lester Platt and Sally Ratcliffe are led to believe that each is cheating on the other.
 * In the novelization of Revenge of the Sith, Palpatine (who is fully aware of Padme's and Anakin's secret marriage) insinuates that Padme is cheating on Anakin with Obiwan. When Anakin visits Padme's residence to confirm these suspicions, he detects signs that Obiwan did visit her. While Padme is able to assuage his temper, Anakin never really lets go of the insidious notion. Later on Mustafar, when Anakin sees that Obiwan stowed away on Padme's ship, he takes it as a sign that Padme had betrayed him. Cue Force Choking.

Live-Action TV
"Harper: I had my mom's private investigator track her down.
 * I Love Lucy has a classic early example.
 * I Carly: Tasha and Freddie, mistaken by Gibby, in iEnrage Gibby.
 * The Jeffersons is another example. In this case, the "other woman" turns out to be an old war buddy of George who recently underwent a sex change.
 * In another episode, Louise finds out George has been giving money and presents to the people in a certain apartment every Christmas, and wonders if he's having an affair or secret children she doesn't know about. It turns out he's just been anonymously helping the family who lives in his old apartment, since he remembers how hard his family had it when he was a kid.
 * In yet another episode, Louise has told George she doesn't want him to work late anymore. George sneaks in from working late and is fact building another store. When caught by Louise, he lets her think that he's having an affair rather than working so much.
 * And another has her catching him in a hotel room with another woman. It's a long story, but it's completely innocent. However, she believes him instantly because she notices that he doesn't display the physical tic that usually tips her off to when he's lying.
 * On Parks and Recreation, Ann thinks Chris is cheating on him because he's so distant, so Leslie investigates. It turns out he's not cheating.
 * Happens in a Tales From the Crypt episode. A jealous and insecure husband overhears his wife planning something with his best friend. As he overhears more of the planning, he becomes more and more suspicious. He ends up killing both and, dragging her body behind him, stumbles into.
 * Played with in Spaced: Marsha, who believes Tim and Daisy to be dating (when they aren't, but merely pretend to be to rent her flat), believes Tim to be 'cheating' after seeing Tim kissing his girlfriend Sophie. This leads to a confrontation where Marsha threatens to reveal the 'truth' to Daisy; however, Tim - unaware that she has seen him, and believing that Marsha is actually talking about a birthday cake Tim has arranged as a surprise for Daisy, completely misinterprets Marsha ("But... you'll spoil the surprise."). Chaos, not unnaturally, ensues.
 * Done on Psych, but not as a major plot point. Shawn's date confesses that she has a boyfriend, but plans to dump him because he's cheating on her. When she lists the evidence, Shawn realizes that her boyfriend isn't cheating; he's actually planning to pop the question.
 * James Wilson on House gets accused of this by House every time he so much looks at a woman (to be fair, he did cheat on two of his wives and told them about it later). This trope is actually the entire B-plot of "Fools for Love", in which it's subverted - it's not Wilson that Nurse Wendy is dating, it's Foreman.
 * In another episode, House and Stacy, his ex, are washing dishes at her place when her husband comes in. House (acting surprised): "It looks like we're washing dishes, but we're totally having sex."
 * There's an episode where a married couple is found to have genital herpes. The wife, naturally, is furious, assuming her husband to be unfaithful. He denies it. House then proposes that one of them could've picked it up in a public toilet. The wife claims she knows about it and always covers the toilet seat. The husband claims he never knew. All seems resolved... then House points out that the husband agreed way too quickly. Turns out the guy really is a cheater.
 * Played with in Friends. Rachel and Phoebe see Chandler meet with an attractive blonde lady and follow them out to a house in Westchester where the two of them spend almost an hour together. They, Joey and Ross leap to the conclusion that Chandler is cheating on Monica when in reality the lady was a realtor who was showing the house. Kind of an Idiot Ball moment, since they immediately assume the worst about their friend.
 * Used in an entirely non-comedic way in Battlestar Galactica. Cally spots her husband Galen having a long and intimate talk with Tory at a bar and accuses him of having an affair with her. He can't exactly tell her that he was really discussing
 * Also, Cally wasn't just imagining things
 * Early in the first season of Alias, Francie suspects that her boyfriend, Charlie, is cheating. Sydney and Francie follow Charlie and find him meeting with an attractive blonde woman, into whose car he loads a bag, before driving off with her, while he has told Francie he has a law review. It turns out that she.
 * In Jeeves and Wooster, this happens to Gussie Fink-Nottle all the time, primarily in the first episode of season 2. This is especially bad, because if Madeline broke off her engagement to him, then Bertie would have to marry her. Either that or explain that he would rather die, which would be bad manners.
 * Done at least twice on Dexter:
 * In season 2, when Dexter and Rita were about to, er, do the deed, Dexters' NA sponser calls... and mentions their road trip, where he confronted his mother's killer, and then they slept together (but did not have sex.) Unfortunately, he let the machine get it, meaning Rita heard everything... and thus, suspected he was cheating. Later on, Lila (the sponsor) and Dexter do have sex, but only after Rita says that their relationship is over. Which apparently she didn't mean, because you know how women can be... so irrational when they think their perfect man is sleeping with another woman.
 * Dexter then confesses to having sex with Lila. Sort of. When Rita asks him to tell her if Dexter had sex with Lila that night, Dexter replies "No... Not that night."
 * And played with in season 3. At first it's played straight when Miguel's wife suspects him of cheating... when, in fact, Miguel can't say where he was because . Then later his wife catches when he did actually decide to rekindle an old romance, albeit for ulterior purposes.
 * Dexter knew about it and was the one responsible for getting Miguel's wife to LaGuerta's.
 * On My Own Worst Enemy, Tom's wife begins to suspect that he's cheating on her when she finds out he was lying about being on a business trip. In fact, Tom's other personality, Raymond, was off on a spy mission, but since Tom doesn't know this, Raymond's bosses have to alter his memories to make him believe he really was cheating.
 * They were actually sort-of rekindling their relationship... then she witnesses Raymond (she thinks it's Tom) shooting someone at night.
 * On Monk, Stottlemeyer asks Monk and Natalie to follow his wife, whom he suspects is cheating. They take pictures of her out with another man, and Stottlemeyer confronts her. The good news: she's not cheating. The bad news: the man is a divorce lawyer...
 * Another episode, "Mr. Monk and the Bully," has Monk and Natalie follow another client's suspected cheating spouse - he suspects it based on her clothing. They follow the spouse, and catch her in a bar with someone else. The next day, he turns up dead. In the end, it turns out that the spouse was not cheating, and Monk and Natalie were following her identical twin sister.
 * Similar thing happened in Smallville with Lana's biological father's wife.
 * In the TV show The Invisible Man, there's one episode where the main characters find a man who faked his death by showing his girlfriend a picture of one of the Agency's scientists, an attractive blonde, and claiming the man was having an affair with her. They also plant other signs--lipstick and perfume on one of his shirts, etc. The girlfriend storms off to confront the supposed cheater, leading the main characters right to his hiding place.
 * Just about every second episode of Bewitched revolved around Samantha mistaking Darrin for doing this, with Endora egging her on.
 * Paul Merton's sketch show had a sketch where his wife (played by Caroline Quentin, his real wife at the time) accused him of having an affair with Gloria Hunniford, because the same night he was out of town on business, she wasn't on TV.
 * Robin on How I Met Your Mother has mistaken two of her boyfriends for cheating: Ted in season two (she had heard second-hand stories of Barney claiming to be Ted) and Barney in season five (who was actually sneaking around to learn more about Robin so he could be a better boyfriend to her).
 * In The West Wing, season 7: Bruno and Vinick find out that Santos discreetly gives a certain amount of money every month to a woman whom he had hired while he was the mayor of Houston, and that the woman has a seven-year old daughter. Bruno and Vinick debate letting the public know about this. Vinick eventually confronts Santos about this;
 * On Chuck the titular character begins dating his college sweetheart, Jill, who walks in on him and Sarah showering (they were trying to get a "poisonous" powder off of their bodies. It turned out to be Hi-C mix). He explains the situation and she is all-too-willing to believe him. This might have had some thing to do with the fact that.
 * Not necessarily..
 * Additionally, after Bryce got Chuck kicked out of Stanford (to prevent him from being recruited for a dangerous mission), Chuck finds out that Bryce is also sleeping with Chuck's girlfriend Jill. Then it turns out that Jill made it up, and Bryce never bothered to set the story straight.
 * In Castle the Victim of the Week was killed over a girl in Cuba, leaving behind a very pissed off wife. Until she learns the girl in question was the victim's daughter. A double whammy followed, as the wife confronted the husband's best friend about the girl, who had no idea what was going on and was trying to calm her down and comfort her... when the husband walked in on them. Guess what conclusion the husband leapt to.
 * From the Wizards of Waverly Place episode "Future Harper":

Alex: Oh, how's the case going?

Harper: Oh, everything's fine. Turns out my dad was just sleeping in the car."

"Kelly: Don't make excuses, Woody. Now I see what's going on. You're busy every night and you won't tell me why. I walk in here and find you two kissing in the back room of a bar. It all adds up. You're in a play and you didn't even tell me.
 * Subverted in Cheers when Kelly finds Woody holding another woman (a pre-Friends Lisa Kudrow!) and immediately jumps to the right conclusion:

Woody: Wait, maybe I was just cheating on you!"


 * In the Tales From the Darkside episode Florence Bravo, a woman eavesdrops on her husband and spots him talking to an attractive woman. As soon as she leaves in anger, it is revealed that the woman is simply a lawyer. Unfortunately, a few minutes after the lawyer leaves, the wife returns and shoots her husband, oblivious to the truth.
 * On Bones, a man with a history of infidelity is killed by . His killer was furious that he'd apparently resumed fooling around, unaware that the young woman he'd been meeting on the sly was his illegitimate child.
 * In Eureka,  thinks his lack of intimacy is because he is seeing another woman. When she asks Jack about it, he says, "Oh, no, no, that's the least of your problems!" The real reason is because
 * In the Warehouse 13 episode "Where and When", it turns out the guy they think has this week's Artifact is meeting his secretary to plan a takeover of the magazine they work for.
 * Part of it has to do with how the guy treats women. Everybody assumes him to be a mysogynistic Jerkass. It turns out that's just a cover he's putting on for the magazine big shots. He actually thinks very highly of capable women and has no problem with them holding his positions in the company. His attitude is actually pretty ahead of its time.
 * In UFO, a flashback to the founding of SHADO has Straker in secret meetings with his new staff. His wife grows suspicious about his late night meetings and discovers him meeting with a female crewmember and makes makes the wrong assumption. Because of the secret nature of SHADO, he can't tell his wife what's going on so she leaves him.
 * In the Hong Kong drama The Drive Of Life, one character saw her friend's husband having lunch with another woman and both were quite close to each other (such as the woman helping the husband try on a jacket). After the character leaves to tell her friend, we find out that the woman was an old friend of his and the jacket she helped him try on was for his son.
 * The central focus of the first Kamen Rider Double Returns mini-film is that Ryu Terui/Kamen Rider Accel is framed for murder...and supposedly has run off with a mysterious woman, which infuriates his new wife Akiko and has her running to file divorce papers. (In reality, she's a pickpocket he was in the process of arresting when everything went to hell; they're handcuffed together and he lost the keys.)
 * Not at all helping is the fact that another character is playing with Akiko's worries for a laugh and because she herself has a crush on Ryu; she's the one who gives Akiko the divorce papers, earning a What the Hell Hero from her grandfather.
 * On Glee, the club's best dancers Brittany and Mike are tasked with coming up with a dance number for sectionals. All's fine and good until Mike's girlfriend Tina confides in Brittany's boyfriend Artie that she suspects Mike and Brittany might be cheating on them with each other. When Artie asks Brittany if she wants to spend more time with him, she avoids the question, saying that she has to rehearse with Mike. Tensions run high all the way to right before the actual competition, and it turns out
 * Later in the season, a blind item in the school newspaper implies that Quinn is cheating on her current boyfriend Finn with her ex-boyfriend Sam, sending Rachel and Finn on a stakeout of the motel where they are supposedly hooking up. While spying on the motel they spot both Kurt and Quinn leaving Sam's motel room, and come to the conclusion that both of them are cheating on their boyfriends with Sam.
 * Happens on The Good Life when Tom and Barbara discover that Margot has not been taking riding lessons like she claimed. They try desperately to keep the secret from Jerry. It turns out she has actually secretly been going to weight loss classes.
 * In Noahs Arc,.
 * Boy Meets World had the "kids think that one of their parents is cheating" version. They find out that their mom is sneaking off to have a romantic dinner with a mysterious man... who turns out to be their dad.
 * Another episode had the parents checking into a hotel to celebrate the wife's pregnancy. At the check-in desk, the husband impulsively shares his news with a random woman, who gives him a congratulatory hug. Sure enough, someone sees this and leaps to the wrong conclusion.
 * On Rumpole of the Bailey, Mrs. Rumpole (Hilda, a/k/a "She Who Must Be Obeyed") thinks her husband's cheating on her. Actually,
 * CSI did this in "Genetic Disorder" with Doc Robbins' wife. Although Brass and Hodges refused to believe the couples' assertions they were faithful, it was proven to be a frame up made to look like she'd been cheating and a random one at that.
 * CSI: NY Danny was Mistaken for Cheating by Internal Affairs. One of his rookie cops shot an unarmed man while they were out for a drink-two guys attacked, and one did have a gun, but she shot the other one. Scared for her career, she told IA Danny told her to lie because they were having an affair, and IA was highly suspicious of a surveilence tape that showed her cozying up to Danny at the bar. Danny vehemently denied it, naturally, but Lindsay had to pressure her to tell the truth and admit what really happened.
 * Brothers and Sisters had the complication of Robert's presidential campaign. An investigator took suspicious photos of him entering a woman's home and showed them to a member of his staff, who happened to be his brother-in-law Kevin. Kevin is torn over his job and loyalty to his sister. In the end it turns out that the woman was actually his therapist.
 * During a case on Bones, Booth and Bones see Sweets' girlfriend trying on a wedding dress and hugging a man. This leads them to assume that Sweets is the other man in this scenario. It turns out she was just the bridesmaid filling if for the bride since they had the same build.
 * Done this way and that on all versions of Law and Order. One noteworthy example has the detectives confronting the husband about his clandestine behavior only to have it turn out he was having an affair with his WIFE and that the sneaking around was an attempt to put the spice back into their marriage. Another had the SVU detectives confronting a man they assumed to be a dead woman's lover, only to have it turn out he was her husband's boyfriend (it's a long story, but suffice it to say, everyone was aware of what was going on, and no one was guilty of murder).
 * Big Love does an interesting version of this as well. Husband Bill and his first wife Barb begin an "affair" (he is technically not supposed to sleep with her on nights designated for the other wives). Second wife Nikki notices his suspicious behavior, concludes that he is courting a fourth wife and is actually pleased, as she thinks it means she will gain a friend and an ally in her clashes with Barb and third wife Margene. When she discovers he's fooling around with Barb, she's hurt and disappointed.
 * On The Dick Van Dyke Show Rob thinks that his coworkers Buddy & Sally are having an affiar, but it turns out they're just moonlighting as a comedy song-and-dance act.

Music

 * The Mecano song "Hijo de la Luna," covered by Sarah Brightman. A gypsy woman makes a deal with the moon to find her a husband, as long as she agrees to give up her first-born child in return. The baby ends up as pale as the moon.
 * Played darkly in Vocaloid's The Tailor Shop on Ebizaka where the tailor was upset that her lover hasn't been coming home to her and finds out he was seeing three different girls on different occasions.

Mythology and Religion

 * Older Than Feudalism: In the Biblical account of the Nativity of Jesus, Joseph initially assumes that Mary's virgin pregnancy was the result of infidelity, until an angel explains the truth to him.

Newspaper Comics

 * A series of FoxTrot strips has Andy convinced that Roger is cheating on her when he's actually at work. ("Listen -- hear that squeaking? You know how my chair squeaks." "Sounds like bedsprings." "Fred, get in here and talk to my wife.") In the last strip, she apologizes for being paranoid and they hug...at which point she plucks a hair from his jacket and asks whose it is. (No, Roger wasn't cheating; he's just balding.)

Tabletop Games

 * Some of the villains of Ravenloft have this trope in their backstory. Anton Misroi caught his wife in the arms of another man, whose shoulder she'd been crying on because Anton was so cruel. Romir Hiregaard leapt to conclusions after seeing his wife and a family friend arm in arm, unwilling to believe that he'd interrupted a waltz lesson. In each case, the wives wound up murdered, and the villains, cursed by the Dark Powers.

Theater

 * Shakespeare used this plot device:
 * It's played extremely seriously in Othello, when the title character believes that he overhears his friend Cassio laughing about sleeping with Othello's wife. Cassio is in fact talking about another woman entirely, and the whole thing had been set up by the villain of the piece in order to mess with Othello's head, but nobody discovers this in time to prevent the usual Shakespearean tragedy ensuing.
 * See also- The Merry Wives of Windsor, Much Ado About Nothing, Cymbeline, and The Winters Tale.
 * This happens to Fiyero and Elphaba in act 2 of Wicked. Somewhat subverted in that Fiyero most definitely did want to be cheating on Glinda at the time.

Videogames

 * In Galaxy Angel Moonlit Lovers, Ranpha suspects Tact of cheating on her with Chitose because she walked in on their hands touching while picking up papers. He spends much of the rest of the story path trying to win her back, eventually dressing up in a ridiculous pink "I love Ranpha" outfit

Webcomics
"Sal: Can I see the ring?
 * A variation occurs in the webcomic Fox Tails, when the Raised By Wolves (Or rather, foxes) amnesiac girl Miyo tells Keen Kotoru's childhood-friend-with-a-crush, Crystal, that she 'slept with him'. She did, indeed, sleep in his bed... while shapeshifted into a fox. The fact that Miyo habitually refers to Keen as 'Master' probably doesn't improve Crystal's view of her either.
 * Subverted in this Order of the Stick.
 * Also defied in this comic.
 * Subverted in College Roomies From Hell, where Marsha walks in on her boyfriend Mike spanking the monkey - which is to say that literally, he has a pet monkey which he is punishing for having messed up the apartment.
 * The webcomic Punch an Pie has this happen constantly to Heather at the beginning of the strip. Her girlfriend Angela seems to think that literally every one of Heather's friends is a possible affair. Angela believing that Polyamory is natural and both being bisexual apparently makes Angela very jumpy about any contact with someone outside the relationship.
 * Used as part of a revenge plot in this Penny Arcade.
 * Almost happened in the Walkyverse, but was averted by one party being Genre Savvy. Danny is talking with ex-girlfriend Sal and mentions that he is planning to ask current girlfriend Billie to marry him.

Danny: Hell no. I know how that works. I show you the ring, and Billie walks around the corner."


 * In Kevin and Kell, when Bruno starts taking classes with fellow herbivores, he meets a rhinoceros named Rachel Einhorn. She is attracted to him at first sight, angering Corrie when she gives him a kiss after saving him from some coyotes and thinking he is cheating on her. It turns out that she, a lesbian, thought he (a "trans-diet" wolf wearing a sheepskin) was a sheep, resulting in him wearing ram horns with his sheepskin from that point on.
 * In General Protection Fault, Craig is thought to be cheating on his wife with Sharon, as Nick and Dexter spy on the two. Similarly, the German, while taking on Craig's identiy during his business trip to Paris with Sharon, makes advaces on Sharon, but when she rebuffs him, realizes that he has misunderstood their relationship.

Western Animation
"Homer Simpson: "I must be the only gullible husband who ever overheard snippets of surprise-party planning, and believed his wife was having an affair!""
 * The Flintstones had an episode where Fred's accidental discovery of a poem dedicated to Wilma, as well as Wilma's strangely secretive behavior, make Fred suspect that Wilma cheats on him. The catch is in the fact that the poem was actually written by Fred himself when he was still a high school student, while Wilma was secretive because she wanted to surprise Fred for his birthday. It doesn't help that a man calls wanting to talk to Wilma, and she acts strangely, like she doesn't want Fred to hear. He becomes suspicious and goes to another phone, to hear her say, "...that's right, Darling, not the only man I ever loved, the only man I ever will love." Fred thinks he's about to lose Wilma to another man. It turns out he didn't get to hear the beginning of the conversation, where the man said to her before she responded, "This is the jeweler calling, on your husband's watch for his birthday, you want the engraving to read 'Darling...'" It was at that point Fred picked up the phone.
 * In another episode, Wilma suspects Fred of cheating, though with better cause: He's coming home late from work, unusually tired, and when she follows him, she finds him in a romantic nightclub him with a very sexy blonde. The blonde is a charm school instructor, and Fred has been taking courses in dancing, small talk, and related matters so as to make their upcoming anniversary more special and memorable. That night was the final exam/dress rehearsal.
 * The Simpsons, "Eternal Moonshine of the Simpson Mind":


 * Another instant was when Homer was returning from France and sees Marge hugging Flanders (she had invited him over for a family dinner). Subverted in that Homer was Genre Savvy enough to know that it's probably not what it is. Semi-Double Subverted because they had both been thinking about having an affair but resisted it.
 * And there was that episode where Homer and Marge was giving marriage counselling to an idol and her baseball player husband. When Homer gave the idol a backrub while eating chicken, her husband on the other side of the door naturally assumed with the moans they were making that his wife was cheating on him.
 * They love subverting this. In another episode Marge listens in on Homer in the next room with his Vegas wife (long story). She hears him says things like, "Oh that's good. Don't stop! Faster, faster! You do this like a pro!" Her response, "Oh no! She's making him a sandwich!" She was.
 * In yet another episode, Marge writes a novel that has echos of real life. Novel-Marge has an affair with Novel-Flanders, which everyone in the town assumes means Marge has the hots for Ned. Lisa is worried that life will imitate art in another way, since in the climax, Novel-Homer character kills Novel-Flanders and himself suffers a Karmic Death. While Homer does chase Flanders to a cliff, it turns out that he just wanted to ask Ned for advice on how to be a better husband, having realized that he's been a real jerk lately.
 * Happens to Reef in the Stoked! episode "Sweet, Sweet Meat Cheat". Fin overhears Reef make a comment about cheating on Lo and assumes the worse. He is actually 'cheating' on the vegetarian diet she put him on by eating franks.
 * The Looney Tunes Show: In "Beauty School", Lola sees a woman (actually Bugs in drag) leaving Bugs' house and getting into Bugs' car and immediately assumes that Bugs is cheating on her.

Real Life

 * A tragic real life example: Rush Dozier in his book Why We Hate, describes an event when a friend of his separated from his wife after several attempts at reconciliation. The man decided to call his wife before moving to another city and an unfamiliar male voice answered the phone. The man rushed to his wife's apartment (it turned out she was alone), broke down the door and fatally shot her, then himself.
 * Things can get odd for adult brother/sister siblings who travel or even just go out to dinner together when people who are unaware that the person has a brother/sister sees them out having dinner together or sharing the same hotel room.