You'll cry and cry and try to sleep.
But sleep won't come the whole night through.
Your cheatin' heart will tell on you."
Adultery. Two-timing. Seeing someone on the side. Having an affair. Cheating. Whatever it's called, the act of having a romantic or sexual affair with someone other than one's established spouse or lover has ever been a source of drama in fiction and in real life. It has brought lovers together, but it has also torn lovers, marriages and even families apart, and it is one of the most common reasons for someone to end up killed. These tropes explore infidelity, the forms it takes, and the effects that it has upon people.
- Absence Makes the Heart Go Yonder: A character starts a relationship with someone else while physically separated from their love interest.
- Accidental Adultery: A character cheated but was tricked, didn't know they were married, believed their partner to be dead, etc.
- Affair? Blame the Bastard: Taking out your anger from your spouse's infidelity on the bastard child born of said infidelity.
- Affair Hair: The discovery of a strand of unfamiliar hair leads to accusations of infidelity.
- Affair Letters: Love letters that document someone had an extramarital affair.
- Bedroom Adultery Scene: An adulterous couple gets caught in the middle of sex by one of their spouses/partners.
- Cheating with the Milkman: A housewife has an affair with service personnel that visit the house.
- Chocolate Baby: When a newborn infant looks nothing like their "dad", implications that their mom slept with another man soon follow.
- Crazy Jealous Guy: The guy who gets mad at the idea of becoming a Cuckold.
- Cuckold: The victim of infidelity, who suffers the misfortune of their spouse being unfaithful to them.
- Cuckold Horns: A pair of horns used to show that a man's lover has been unfaithful.
- A Deadly Affair: Someone ends up dead, whether it's the perpetrator(s), the victim, or the baggage holding the affair back.
- Emasculated Cuckold: Having an unfaithful wife is a blow to a man's power, masculinity, and status.
- A Family Affair: The cheater sleeps with their partner's relative.
- Good Adultery, Bad Adultery: In a work with multiple instances of adultery, the adulterer is portrayed sympathetically in one instance and evil in another.
- Lipstick Mark: Lipstick on your clothing, collarbone, or cheek reveals an affair.
- Love Forgives All but Lust: Someone is willing to forgive or deny all their partner's faults or crimes except adultery or wandering eyes.
- Mal Mariée: A young woman unhappily married to an older man, who often cheats on him with a man her own age.
- Mistaken for Cheating: Someone mistakenly believes their partner is cheating on them.
- The Mistress: A relatively long-term lover whose partner is married to someone else.
- Netorare: Cuckoldry as a genre of Japanese porn.
- Plot-Inciting Infidelity: When the plot of a story is kickstarted by having the protagonist catch their partner cheating on them.
- Playing Sick: For the version of the trope where one member of a couple (normally, a man) is on the mood, but the other (normally, the woman) feigns a sickness (normally, a headache) in order not to have sex. Usually, this will happen repeatedly, and it's implied (if not explicit) that she doesn't really love or isn't attracted to him, or even that she's having an affair with someone else.
- Remarried to the Mistress: A man marries the same woman with whom he cheated on his ex-wife.
- Scarpia Ultimatum: A character sleeps with a villain in exchange for sparing their partner.
- Secret Other Family: A mistress plus kids—a whole second family.
- Serial Homewrecker: A character who seeks out romantic or sexual partners who are already in relationships.
- Sex with the Ex: In cases where one or both exes have new relationships but still sleep together.
- Sleeping with the Boss's Wife: Screwing around with your employer's spouse.
- Sympathetic Adulterer: Cheater portrayed sympathetically.
- Two-Timer Date: A person schedules two dates at the same time and goes between them. Usually Played for Laughs.
- Woman Scorned: A woman becomes violent upon discovery of being cheated on.
- Death by Woman Scorned: And sometimes, the man or other partner does not survive her retribution.