Death by Woman Scorned

He'd go out every night looking for himself... and on the way... he found Ruth, Gladys, Rosemary... and Irving. I guess you can say we broke up because of artistic differences. He saw himself as alive...and I saw him dead.

—Mona, from "The Cell Block Tango," Chicago

Alice is dating or married to Bob. Alice finds out that Bob is sleeping with Carol. Alice then kills Bob for cheating on her. This may be presented as a justified act, even if it is a serious crime. He done her wrong. While the same scenario is a common dramatic plot with both genders, modern depictions are often more sympathetic to Alice shooting Bob-the-cheater than Bob shooting Alice-the-cheater.

In Real Life many cultures have tended to go easy on the husband's killing either a cheating wife and/or the man she was cheating with. Not so much in the modern Western world, though, and stories produced from that perspective don't usually treat it as justified in anything more than a passing reference/joke, which is why most examples here come from songs. A full story involving someone killing their straying lover usually has to admit that this is a bad thing to do.

See also Manslaughter Provocation—until 2009, in Britain, killing your wife for infidelity was manslaughter, not murder.

As a Death Trope, Spoilers ahead may be unmarked. Beware.

Examples of Death by Woman Scorned include:

A common theme in country music.
A common plot element in crime television dramas, although the murderers are less likely to be seen sympathetically in such stories.
Played with in a Star Trek: The Next Generation episode where the plot goes both ways - a male character sees himself cheated on, murders both parties, and commits suicide, then a female character goes through the exact same scenario and reacts the same way. In actuality, both characters were being caught up in the psychic playback of events that happened to someone else in the past. And that someone else was not presented as justified, but as disturbed.
Unpleasantly required as part of the Goblin newbie zone in World of Warcraft regardless of gender - you have a romantic partner, that romantic partner then leaves you for someone else, and you have to hunt them down and rip out their cheating heart.
- Mind you, the one they've left you for is also trying to sell you into slavery, so it's a bit more understandable.
The School Days media series of games, anime and manga have this going on in some of the bad endings, when it's not Murder the Hypotenuse.
In Vorkosigan Saga there is an example of Death by Man Scorned where Aral kills two men who had seduced his first wife. It is presented more sympathetically because it was in a Duel to the Death.

Woman kills Man

Three of the "Six Merry Murderesses of the Cook County Jail" from Chicago fall under this trope. In fact, the former trope namer (He Had It Coming) comes from their chorus in the "Cell Block Tango," where they give their accounts of how their husbands died for "crimes" like popping their gum. Only Hunyak turns out to be innocent.
- The reasons for each were:

1. 1. Liz's husband popped his gum (which she says is an irritating habit) one too many times after she'd had a long day.
  2. Annie found out her boyfriend was not only married, but was a Mormon with six wives.
  3. June was (perhaps wrongly) accused by her husband of cheating on him with the milkman.
  4. Hunyak DIDN'T kill her husband, but was thrown in jail with the rest because no one could understand Hungarian.
  5. Velma walked in on her husband doing the "spread eagle" with her sister Veronica.
  6. Mona found out her boyfriend's long walks at night were really an excuse to visit his other girlfriends and eventually a boyfriend.

- A later scene had an heiress shoot her husband when he was in bed with two women. His Implausible Deniability just adds What an Idiot! to this.
- Despite being the original trope namer, the show doesn't really give the impression that what these women did was acceptable... just that they can manage to manipulate events to get away with it.
The extended version of Garth Brooks's "The Thunder Rolls" (though the video depicts the husband as being abusive as well as adulterous):

She runs back down the hallway
To the bedroom door
She reaches for the pistol
Kept in the dresser drawer
Tells the lady in the mirror
He won't do this again
'Cause tonight will be the last time
She'll wonder where he's been

The first published version of the Murder Ballad "Frankie and Johnny" ("He was her man/But he done her wrong") appeared in 1904, making this Older Than Radio.
This trope is the entirety of Oxygen's Snapped. Most episodes covers a Real Life case of an abused and/or cheated-on woman who killed her husband (sometimes father). They try not to paint the women in a sympathetic light, but the show still has a "You go girl" kind of feel.
- Sometimes the husband is a saint and the woman is simply tired of being married but doesn't want to go through a divorce, or wants his life insurance policy, or the woman was actually a sociopath. These episodes don't count, though - they're just plain ordinary murder and not relevant to this trope. Women do sometimes kill people for reasons other than "bad men".
This is the setup for the Roald Dahl short story "Tales of the Unexpected Lamb to the Slaughter", infamous for its extremely clever Twist Ending. Admittedly, it's stepped up a notch as the husband explains to his wife—who's pregnant with their first child—that he's going to leave her for reasons implied to be this trope, ending with "And I know it’s kind of a bad time to be telling you, but there simply wasn’t any other way. Of course I'll give you money and see you're looked after. But there needn't really be any fuss. I hope not, anyway. It wouldn't be very good for my job." You might be tempted to konk him too.
Cher's Dark Lady.
Lil' Kim has killed at least 2 boyfriends in her songs.
Anna Russell's songs "Dripping With Gore" and "Two Time Man" are (mild) parodies of this trope as used in country music.
"If You Hadn't, But You Did" from the musical revue Two on the Aisle has a verse beginning in soap-opera-style bathos and ending with a gunshot. It then turns into an angry List Song running down the reasons for saying goodbye to her husband, most of them having names like Geraldine and Kate.

Man kills Woman

Garth Brooks's "Papa Loved Mama" is presented as comedy. This version is sympathetic to both the lonely, cheating mother and the cuckolded, murderous father.

Papa loved Mama
Mama loved men
Mama's in the graveyard
Papa's in the pen

The ambiguous ending of George Jones' "Radio Lover" can be interpreted as this, involving a cuckolded DJ husband who comes home to catch his wife in bed with another man, and then sings the song's chorus, "The last words they ever heard."
Subverted in The Shawshank Redemption: Andy's wife was cheating on him, and he goes to jail for her murder. He's innocent, though.
The rap song Scandalous Hoes II, which ends with murdering the woman for cheating, presented as completely justified
Possibly subverted in The Darkest of the Hillside Thickets' "Jimmy the Squid". Jimmy is accused of killing his mate for sleeping with another squid. He says he's innocent.
Tom Jones' Delilah.
Hey Joe, recorded by a number of artists
Willie Nelson's Red Headed Stranger
Warren Zevon's A Bullet For Ramona
Weirdly appears on Rome when Vorenus finds out his grandson is in fact his wife Niobe's son by another man. According to Roman custom at the time it was not only Vorenus' right to kill her for her infidelity, but it was also what honor demanded (and Vorenus is constantly shown to put Honor Before Reason). He grabs a knife but doesn't seem like he will be able to actually kill her, so she flings herself off a balcony and takes her own life as a final act of love.
In Oscar Wilde's "Ballad of Reading Gaol," this is the condemned prisoner's crime.

He did not wear his scarlet coat,
For blood and wine are red,
And blood and wine were on his hands
When they found him with the dead,
The poor dead woman whom he loved
And murdered in her bed.

The third verse of Dr Dre and Eminem's "Guilty Conscience" has the two arguing as a man's conscience on whether or not to kill his cheating wife and her lover (Dre tries to talk him out of it, but Slim Shady is goading him to go ahead). They both agree to do it after Slim calls Dre out on his own past ("You gonna take advice from somebody who slapped Dee Barnes?").
Appears to be the case in Nick Cave & the Bad Seeds "We Came Along This Road". The song's lyrics start with "I left by the back door, with my wife's lover's smoking gun" and then describe the protagonist going on the run.
Richard Marx, "Hazard", maybe. The male character's accused of it, but the truth is intentionally ambiguous.
Played with in Reba McEntire's "The Night The Lights Went Out In Georgia". A man finds out that his wife's been the town bicycle while he's been gone, and goes to kill her and his friend who she was last cheating on him with. He gets arrested for it, and as the title suggests, gets the death penalty. Subversion: the husband didn't do it. His little sister got to the cheating wife and the friend first.

Attempted Murder

In Adam's Rib, a wife shoots her husband after finding another woman in his arms, but he survives. Her defense attorney, Amanda Bonner, gets the jury to excuse her actions under the Double Standard grounds that a man shooting at an unfaithful wife would not be judged so harshly.