Bob is a villain, but his wife/girlfriend Alice (it's pretty much Always Female) refuses to believe any accusation of wrongdoing on Bob's part, and prefers to believe in a vast conspiracy designed to discredit him, even if she comes across Bob beating a man to death with a shovel. However, if/when Bob cheats on her, flirts with another woman, or possibly even talks to another woman, she instantly becomes his worst enemy, willingly telling the heroes every last crime he (or they) committed and sparing no expense to see him hang. This trope can carry some Unfortunate Implications of gender-based vanity towards females being willing to forgive any slight from their mate as long as it doesn't threaten their status as the prized lover.
See also Arson, Murder, and Jaywalking when the other offenses make the cheating laughable in comparison, Woman Scorned for revenge in general, and All Girls Want Bad Boys when its women being okay with having evil-doers for mates until they betray them. Subtrope of The Last Straw.
- Mean Girls: Aaron willingly dates Regina, who is spoiled, shallow, selfish, rude, and sometimes downright cruel, even to the people she calls her friends. He doesn't seem to mind any of this, and when asked why he likes her, he defends her by saying "everyone has good and bad in them, she's just more upfront about it than most." But when it turns out she's cheating on him, that apparently is too far, and he immediately breaks up with her.
- Marriage Story: Zig-Zagging Trope. Nicole talks to her divorce lawyer, telling her the story of her marriage and why she wants a divorce now. At the end she offhandedly mentions a suspected infidelity. To her, this is a footnote, a largely unimportant detail in her reasons for wanting a divorce. However her lawyer lights up upon hearing that, knowing that is can be used to win the case.
- Midsommar. Dani and Christian are extremely unhappy together, but Dani patiently puts up with his gaslighting, criticism, and general coldness towards her...until she sees him cheating on her with Maja, in a position the Harga might've put her so she could finally have enough of Christian. Shortly after that, in her new position as the May Queen, Dani decides to have Christian burned alive and sacrificed.
- In This Day, Laura puts up with all of Massimo's shortcomings until she walks in on him having sex with his ex Anna (or so she believes). She promptly leaves without a word, saying she can't look at him the same and that she thinks marrying him was a mistake.
- Sherlock Holmes:
This girl had been devoted to him. A man always finds it hard to realize that he may have finally lost a woman’s love, however badly he may have treated her.
- In The Adventure of the Illustrious Client, Holmes must find a way to prevent a marriage with a rich young woman and a depraved baron, who has already convinced her that a man of his quality has many enemies, who are happy to spread rumors about his philandering and having killed his first wife. When one of his victims fails to convince her, Holmes looks for a diary in which he counts his conquests (his "lust-diary", as Holmes calls it). Once Holmes delivers it to her (and the baron is disfigured by said former mistress), the marriage is called off.
- In "The Problem of Thor Bridge", Gibson's Costa Rican wife is fanatically in love with him, even though he's long ceased to love her. Then when she finds out he's making advances to the governess, and even though the governess refused him, the governess has more influence over the husband than the wife does, so the wife comes up with a plan to kill herself and frame the governess for it. It almost works, and Holmes hopes Gibson will be less of a Corrupt Corporate Executive afterwards.
- In The Hound of the Baskervilles, Stapleton's wife, who he passes for his sister, was his reluctant partner in crime until she discovered he was making advances towards another woman (whether or not he actually intended to propose is not known), which finally caused her to snap, forcing him to tie her up before she can warn the heroes. Too bad for him she'd already gone out to remove the pegs that marked a safe route through the moor. Stapleton himself nearly screws up his own plans when he finds himself unable to not act like a Crazy Jealous Guy one seeing her being wooed by Sir Charles (despite her not looking happy about it).
- "The Musgrave Ritual": Holmes figures out that the butler had an accomplice (who left him to die in an underground vault), most likely the servant he'd been in a long relationship but had just dumped for someone else.
- One Charles Exbrayat novel features the murderer's wife caring less about the fact that her husband killed three people and more about the fact that he had a mistress.
- Taken even further in one Hercule Poirot short story: the man is (separately) romancing both a young woman and her aunt. He's trying to get money from the old lady and claiming that to prevent people from looking down on them both, he'll pretend to be in love with her niece. So when the aunt and niece have a fight (neither suspecting the man), the aunt sends Poirot a letter asking him to investigate.
- An interesting variation in the novel Rebecca by Daphne du Maurier. The female lead spends the first half of the book moping because she thinks her husband is still in love with his (dead) first wife instead of her. Cue wangst. But then it's revealed that he hated his first wife, and he actually murdered her. Murder? No problem! He doesn't love that minx; he loves me! (To be fair, it's presented like his first wife was The Vamp with absolutely no moral code and masterfully provoked him to do it... but still.)
- Downplayed in Gone Girl. Amy is a sociopath, but in her mind, she accepted moving from New York to rural Missouri, Nick losing his job, her parents draining her trust fund, and Nick buying the Bar with her money...until he cheated on her with Andi. That was when she started plotting to frame him for her murder. However, she didn't so much as "forgive" him for the rest but put up with it.
- Judge Dee: Started a massive chain of crime in The Chinese Bell Murders: The ruthless businessman Lin Fan had murdered his business rivals, who happened to be his wife's brother and father, but she did nothing against him. But when Lin Fan raped his sister-in-law, his wife went into full Woman Scorned mode (especially tragic as she finally gotten pregnant, and she had been a calming influence on him, and the judge believes Lin Fan's actions were just a passing whim rather than actual attraction), culminating in arranging for Lin Fan to murder her son (the son he didn't know about with her).
- Paul of The Green Mile tell about a female inmate, Beverly McCall, who accepted being beaten by her husband but who, upon learning he cheated on her, took a razor and cut his genitals, leaving him to bleed to death.
- Averted in Old Man's War. When John is telling Jane about his late wife Kathy (Jane is a sort-of clone of Kathy), he admits to having cheated on her once. Except, Kathy was of the opinion that cheating was a physical failing, not a mental one. But he did almost end their marriage because he lied about it, and that's something Kathy couldn't abide. It took a lot of effort for John to get her to forgive him.
- In "The Lady, or the Tiger?", the princess who holds her lover's life in her hands agonizes over whether to save him — because it will mean handing him over to a woman who may or may not have her eyes on him (and he might even return her interest).
- Beverly Hills, 90210: Donna stayed with Ray after he hit her, but dumped him when she found out he cheated on her.
- In Brooklyn Nine-Nine, Jake is chasing after a mobster who escaped a sting operation he masterminded, who he states is worse than any of the people they did catch. They interview his mistress to see if she knows where he is and she protects her violent criminal boyfriend up until Jake reveals that he has another mistress: her sister.
- Cheers: Norm applies this philosophy to himself.
Norm: I don't know my wife's favorite color, I don't know when her birthday is, I don't know when our anniversary is. We never spend any time together. But I don't cheat on her. That may not sound like much to you, but to me it's the difference between being a bad husband and being a bad person.
- Dexter: One short-lived villain, Nikki, had no problem robbing and murdering tourists with her boyfriend Johnny until she found out he was cheating on her.
- Midsomer Murders: One episode ends with The Reveal that an abuse victim being sheltered by another woman had been faking her injuries (and was in cahoots with her husband all along), but the woman hiding her didn't testify against her out of love, leading to jail time for her and the couple fleeing the country scot-free. Until Barnaby sends her a photo of the couple clearly enjoying life with a new mutual girlfriend, and later gets a call implied to be the woman spilling the beans.
- That '70s Show has an example in which the love is non-romantic. Red dotes on Laurie despite the fact that she's an ungrateful mooch. It seems that nothing she does can get her father to be upset with her. Until she moves in with her boyfriend.
- Mass Effect: Kaidan Alenko can have his entire moral compass changed with just a persuasion check by a renegade female Shepard who is romancing him. All it takes is one conversation to convince him that instead of aliens being jerks and saints like the rest of humanity, they're instead "damn aliens who like to get technical". He'll advocate for leaving thousands to die because they're aliens, but heaven forbid Shepard move on in Mass Effect 2. He'll repeatedly say she cheated on him in Mass Effect 3 even though he had admitted in an email to her that he had been dating a doctor before then.
- Family Guy: Peter develops amnesia and doesn't remember his family, including his wife Lois. She's understanding about it until he brings home his new girlfriend.