Friend Versus Lover

"Jes: How about this, you pay for cable and you get one night a week with Ian. Dom: Tempting, but you're lowballing me. Ian: As the commodity being traded, do I get any say in this matter? Jes & Dom: No. Ian: [Puppy Dog Eyes]"

- Three Panel Soul, On Security Deposits

When a character's best friend (possibly a Heterosexual Life Partner) and the Love Interest have a rivalry over "ownership" of the third party.

Hilarity Ensues. Except when the friend is poisonous, the love interest is clingy or psycho-possessive, one or both might decide to Murder the Hypotenuse, leaving the other a Cassandra Truth. Less murderously, both start a secret war for the affection and attention of the third party, trying to slander the other while seeming innocent. By the end one or the other usually reveals they were less than ideal as a friend or lover and get cropped out of the picture.

When it doesn't come to blows, they either reconcile their differences... or draw up a "custody" contract that is ludicrously complicated. On occasion, the third party will call them out over being treated like a commodity... before being shushed so the grownups can talk.

When the third party manages to put their foot down, they might manage to mediate a solution. However if both descend far enough in this petty politicking, the third party may well dump them both as an incentive to make them get over themselves. Fandom often comes up with its own, sexier, solution to the dilemma.

For some reason, the third party is usually a guy, the love interest a girl, and the friend another guy. Only rarely are the gender roles switched.

See also Yoko Oh No, when a whole group of friends dislike a new lover.

Anime & Manga

 * In Skip Beat, Ren (mutual crush) and Moko (best friend) sometimes act like this towards Kyoko. On Kyoko's birthday, they were secretly trying to figure out who could get her a better present.
 * Averted, Ren was taking the mature route of "it doesn't matter which gift is the better" and Moko originally didn't know it was Kyoko's birthday but had gotten her a gift anyway.
 * Though, that might have been because of Ren's confidence in his present, considering he secretly gave her a crystal.
 * In Baka to Test to Shoukanjuu Shoko (the love interest) thinks she and Akihisa (the best friend) are in this for Yuuji's affection. In reality, Akihisa doesn't see her like this and is willing to sell Yuuji out so he can win this competition against her.
 * In Pandora Hearts Gilbert and Alice sometimes do this over Oz.
 * In all of a moment, the relationship between Shirley (love interest) and Rolo (clingy surrogate brother) of Code Geass becomes this when.
 * Yui and Tamahome over Miaka in Fushigi Yuugi ( Because Yui has a crush on Tamahome, too, and wants him for herself.)
 * In Tiger and Bunny, reading between the lines will enable you to see the antagonism between Karina (love interest hopeful) and Barnaby (partner and close friend) over Kotetsu -- especially noticeable in post-timeskip episodes and heavier on Karina's end than Barnaby's. It's lampshaded by Word of God and in the 2nd drama CD; but since Kotetsu has yet to so much as consider Karina's potential to be his girlfriend, an out-and-out feud was averted.

Comic Books

 * Played for Laughs in Archie Comics, with an unexpected conclusion. Archie tries to take Veronica out to a movie, while discussing Jughead seemingly getting too attached to Archie. The couple thought they have lost Jug, only to run back into him when they were at the theater. An argument rises up, and all three were kicked out because of the commotion. Archie makes up an excuse to get away from both of them, and when out of earshot he feels nothing but woe over being popular.

Film

 * The 2009 Sherlock Holmes movie has the tension between Mary (who's willing to share) and Holmes (who isn't) both wanting Watson at its center.
 * My Best Friend's Wedding had this, with a little overlap in Love Triangle. Julianne and Michael made a marriage vow that, as best friends, if neither was married at age 28 they would marry each other. When Michael tells her he's marrying Kimberly, she panics and does her best (worst?) to break them up so she doesn't end up a spinster.
 * Pretty in Pink has two of these: Ducky/Andie/Blaine and Blaine/Andie/Steff - the latter with the twist that Steff also tries to get together with Andie, leaving him barely any time or energy for his supposed actual girlfriend, or exuding general predatoriness.
 * The plot of A Fairly Odd Movie: Grow Up, Timmy Turner! is about Timmy having to choose between remaining a kid so he can keep his fairy godparents or growing up so he can pursue a relationship with Tootie.
 * Although The Lion King's song "Can You Feel the Love Tonight?" is mostly just a romantic montage between Simba and Nala, it begins and ends with Timon and Pumbaa, Simba's best friends, lamenting the fact that they will lose him if he goes back to the Pridelands.

Literature

 * Sparhawk (from the Elenium trilogy by David Eddings) has gotten this treatment more than once. A dedicated member of the Church Militant, his wife basically negotiated with the church head to get his hand in marriage, and on numerous later occasions, when someone has needed his services in his area of expertise ('saving the world from Evil Gods', mostly) they have had to negotiate with his wife to 'borrow' him. And yes, he even used the "Don't I get a say in the matter?" line. With the predictable result.
 * Justified, since Sparhawk is also the Prince Cosort and Champion of Elenia under command of his wife the Queen, and for political reasons she can't let the Church order her husband around while ignoring her authority.
 * Replace the "friendship" side of the equation with "adoptive familial relationship" and you have Jean Valjean, Marius and Cosette in Les Misérables.
 * Jeeves spends a lot of the Jeeves and Wooster stories getting Bertie out of romantic entanglements. This is mostly because Bertie wouldn't be happy with the type of girls he attracts anyway, and often ends up engaged by accident; however, this trope is clearly in play as well.

Live Action TV
"You have known him since you were squealing infants together. You will always know him better than I do!"
 * Sometimes touched on in Scrubs, but it usually ends up that they're all ok with it.
 * Dawson's Creek started out with Jen/Dawson/Joey, and when that went the way of AbortedArcs, Pacey/Joey/Dawson.
 * Sean, Christian and Julia on Nip/Tuck have gone a few rounds on this.
 * Happens in House almost every time Wilson gets a girlfriend. The current one is fighting a secret war with House to see who'll win in the long term...
 * When Wilson was with Amber, House actually did come up with a 'custody contract,' which Amber reluctantly agreed to and later added 'penalty clauses' to.
 * On Star Trek Deep Space Nine, Bashir and Keiko occasionally have this sort of conflict over O'Brien.
 * Buffy had Willow, who was Xander's best friend since kindergarten, and Anya, his girlfriend, occasionally clashing over him in Season 5.

"Wash: I mean, I'm the one she swore to love, honor and obey. Mal Listen--... She swore to obey? Wash Well, no, not... But that's just my point! You she obeys! She obeys you! There's obeying going on, right under my nose! Mal: Look, Zoe and I have a history. She trusts me. Wash: What's that supposed to mean? Mal Don't mean a thing, but you're making out like she blindly follows my every word. That ain't true! Wash: Sure it is! Mal: Not so. There's plenty orders of mine that she didn't obey. Wash: Name One! Mal: She married you!"
 * Buffy influence over Riley Finn causes resentment among his military buddies, particularly Forrest.
 * Notable for its aversion in Merlin. Arthur and Merlin are Heterosexual Life Partners, but when Guinevere starts to catch Arthur's attention, Merlin couldn't be more delighted. This poses quite a problem for the slashers considering Merlin and Guinevere are Like Brother and Sister, and more often than not it is Merlin encouraging Gwen to spend time with Arthur.
 * Merlin even takes on a Die for Our Ship mentality toward anyone who looks as though they're a possible Love Interest for either of them.
 * In Eastenders, Roxy and Syed are not fans of each other at all, much to Christian's dismay.
 * This was the central plot of the Frasier season 10 finale, where Frasier's best friend Roz absolutely despises his new girlfriend Julia and believes that she is a terrible match for Frasier, to the point of telling Frasier she's evil and has him brainwashed, telling Julia to her face that she's not good enough for Frasier, trying to sabotage the relationship by trying to trick Julia into thinking Frasier's two-timing her, cornering her and telling her to stay away from Frasier or else, and even threatening her with physical violence. In the end, after Frasier refuses to listen to her pleas to take her advice and dump Julia, Roz point-blank tells him that "It's her or me, Frasier, tell me now or I swear to God I will walk out that door and I will not come back." The whole debacle ends in a rather nasty deconstruction of the trope: instead of reading this as a difficult choice between an old friend and his trust in her advice, and a new lover and his belief in her worthiness, Frasier is (quite understandably) so outraged by Roz's meddling that he impulsively chooses Julia in a fit of pique and Roz does walk out of his life (though they make up next season).
 * iCarly had an episode where Sam started dating a guy and repeatedly blew Carly and Freddie off as a result.
 * Another episode had Sam as the third wheel when, dateless on the night of a dance, she seeks out Carly and Freddie only to be dejected to find them having a romantic moment together. Whether or not that was this trope or another one was left ambiguous.
 * This ended up happening to Carly herself when Sam and Freddie briefly dated.
 * Ted and Lily on How I Met Your Mother occasionally had this kind of conflict over Marshall, but tended to act out their possessive and jealous impulses on Marshall rather than each other (partly because they themselves were really good friends as well). On Ted's side, this came to a head in the episode "The Duel", where Ted panics that Marshall will abandon him and strikes back at this perceived encroachment on his territory by demanding that Marshall give him the apartment, which quickly devolves into a major argument and a frickin' sword duel between the two. They make up quickly though, partly because the sword duel was just that awesome.
 * The episode "How Lily Stole Christmas" hinges on a variation of this conflict between Ted and Lily. Lily thinks Ted has been mad at her for hurting Marshall when she ran off to San Francisco and that since Marshall has now forgiven her, Ted should too. Turns out he is still mad, but more because she was also supposed to be his friend too, but never even called Ted during her absence. She had apologized to Marshall, but not to her other friend she left behind (the one who had to clean up the mess she made of Marshall by leaving)
 * Wash and Mal in Firefly.


 * An episode of Men Behaving Badly dealt with this (It was even titled "Your Mate Vs. Your Bird").
 * On Awkward, Matty is secretly dating Jenna and comes across a problem when his best friend, Jake, develops a crush on her.

Newspaper Comics

 * This happened in an old Bloom County strip. Cutter John was with his animal friends when his girlfriend came over and borrowed him for an extended interlude. His friends were rather indignant at this.
 * All the time in Archie Comics when Jughead will get into a fight with Veronica over Archie.
 * Sometimes Jughead gets into a fight with Betty over Archie, but usually Jughead will team up with Betty against Veronica because, unlike Veronica, Betty is willing to share Archie with him!
 * In Garfield, after Jon started dating Liz, Garfield felt jealous of her, but eventually got over it.

Theater

 * In Gilbert and Sullivan's Iolanthe, Lords Mountararat and Tolloller both want Phyllis. They were friends from their childhood. Eventually, Phyllis persuades them that this rivalry is not worth the cost of their friendship, and to both give up their desire.
 * The Merchant of Venice has two cases:
 * In the main plot, Bassanio's friendship with Antonio versus his romantic relationship with Portia. This is an extremely mild case, but is often played up for the sake of drama in performance.
 * In the subplot, Lorenzo is in love with Jessica, and Launcelot is Jessica's friend, who acts as go-between delivering their love letters and helping them to carry out their elopement. All three characters aren't seen together until very late in the play, when Jessica is married to Lorenzo; at this point they've clearly become a case of this trope, with Lorenzo joking that he's jealous of Launcelot and the two proceeding to rank each other out.

Video Games

 * In Disgaea 4: A Promise Unforgotten, Fenrich and Vulcanus are frequently at odds with each other in regards to Valvatorez. Then again, the game tosses around enough hints to suggest that it might just be a straight-up Love Triangle.

Webcomics

 * Gunnerkrigg Court: Antinomy is jealous of Alistair who strikes it off so well with Kat. She stifles it and insists they get a proper farewell, leading to their discovery that Alistiar is being turned into a bird, permanently.
 * A playful version where both the friend and the lover are female appears in this Questionable Content strip.

Web Original

 * In the Homestar Runner cartoon Date Nite, Strong Bad acts like this when the Cheat goes out on a date with Marzipan, and ends up teaming up with a jealous Homestar to try to sabotage the date.

Western Animation

 * On Jimmy Two-Shoes, Jimmy's Poisonous Friend Beezy and his Yandere Heloise are constantly at war for his attention. The only reason they remotely tolerate each other is to stay around Jimmy.
 * In X-Men: Evolution between Kurt Wagner (Nightcrawler) and Lance Alvers (Avalanche) about Kitty Pryde (Shadowcat). Brought Up to Eleven in some fanfics.
 * Scooby Doo Mystery Inc has Shaggy caught between Scooby and Velma. It's largely his own fault, though: he blamed his own fear of going public with their relationship on Scooby even though Scooby already knew and seemed to approve... until Shaggy tried sneaking off to prom without telling Scooby what was going on, seemingly ditching him in the process. Then he actually started disapproving of the relationship.
 * In Spider-Man: The New Animated Series, it was between Peter and Talon. As Spider-Man, he knows Talon's identity and was weary of her when Harry started dating her. Of course, he couldn't say anything without revealing his secret.
 * Daria often featured this with Daria and Jane's relationship with Tom--as in, each girl got to be the third wheel when Tom dated both in successive years.
 * Kid vs. Kat presents a passive, one-sided example with Coop's Action Girlfriend Fiona and his Heterosexual Life Partner Dennis. Dennis initially dislikes Fiona because she unintentionally distracts Coop from his usual "defeat Kat" plans, and because Coop spends more time with her than with him. However he warms up to her in later episodes, even saving her from Coop's Yandere Stalker with a Crush Phoebe in "Birthday Bashed".