Two characters that used to be a couple broke up. They got bored of each other or argued too much, he just wouldn't put the seat down, she used too much toilet paper, whatever. Emotionally or mentally they didn't think they were right for each other. Sexually, however, they still get along just fine.
They may only get to kissing each other or get further than that, but as long as they're reinitiating a physical relationship it's fair game. It can naturally take on a variety of forms, as people are complicated; it may just be sex and friendship, it may be a pattern of hooking up, swearing to never see each other again, and hooking up again, or they could go back into a relationship.
May lead to getting back together, particularly if it starts after a separation or after they've moved on to other people for added drama/comedy. Naturally, a common sitcom trope.
- Lupin III: Lupin and Fujiko have been known to shag on occasion, due to the on-again off-again nature of their relationship.
Fujiko: "We're friends, yes... we've been enemies too. On some occasions, we've even been lovers."
- Fujiko lampshades it in the Manga dub of The Castle of Cagliostro, while explaining her history with Lupin, to Clarisse:
- The most notable instance being in The Secret of Twilight Gemini, where they get it on twice, despite Lupin's interest in Lara. They're interrupted the first time, by Sadachiyo and his men. The second goes off without a hitch. Lupin bangs her in the file room of a Moroccan police station!
- Pilar walks in on her parents Jerrica and Rio after this in the Jem fic Starlight Is For Always, confirming that they're back together. Pilar is more happy than unnerved because they've been broken up since before her birth.
- In The Wedding Singer, Adam Sandler's ex-girlfriend takes advantage of his drunken blackout to have a one-night stand with him. He rejects her once he sobers up the next morning.
- In Hatchet II, two of the hunters hunting Crowley used to be married, causing tension between them. Eventually they end up alone together, and decide to have a shag in the middle of the woods.
- There is an old joke about a woman who visits a friend she didn't see for years, and sees several children who look just like the husband their mother divorced years ago. When questioned, said mother says "He sometimes visits in order to apologise".
- The Book of Joe has Joe and his former high school girlfriend Carly reconnect when he revisits town. It is implied that they'll rekindle their relationship following their night together.
- Used as a plot device in the Pilot Episode of Cheers, where Diane's fiance jilts her so he can run off on their planned honeymoon with his ex-wife, thus forcing her to work at Sam Malone's bar for several years' worth of UST.
- Friends: Ross and Rachel were guilty of this, several times, during break-ups, and when Monica and Richard break up the second time she offers him one last night together.
- In The Wire McNulty's estranged wife Elena propositions him after a make-peace date. This leads him to think they can get together again; however, it proves to be a one-time occasion.
- The Golden Girls had an entire arc of it with Dorothy and Stan, leading up to the intended, but called off, re-marriage.
- Used to definitely break up Rachel's relationship at the end of the first season of How To Make It In America. She ponders over breaking up with her boyfriend, gets drunk, sleeps with her ex Ben, then tells her current boyfriend it's over and underlines how over it is by mentioning she slept with Ben.
- Scrubs: Dr. Cox started sleeping with his ex-wife Jordan, who is one of the few people with a strong enough personality to keep up with him. After about a season and a half of this just loathing himself and sabotaging any attempt at a new relationship, they get back together officially when Jordan becomes pregnant and remain together officially unmarried the rest of the series.
- Subverted in a later episode, when it's revealed that, due to a legal mix-up, they were never actually divorced (they signed the wrong papers). This ends up ruining their relationship, until Cox gets on one knee at the end of the episode and asks Jordan to divorce him. She happily accepts, and they have a divorce ceremony. The witnesses just look at Cox and Jordan's kid and Carla tells him that he'll never be normal.
- My Name Is Earl: Earl's wife Joy divorced him in the first episode and those early episode had a very rocky relationship. When Earl accidentally ruined Joy's marriage to Darnell he set out to make it up to her, which managed to get them back together as friends and accidentally sparked a night together, forcing Earl to need to make things up to Darnell.
- Darnell actually wasn't pissed off at Earl for sleeping with Joy. After all, Darnell did it to Earl first.
- The Big Bang Theory: Leonard and Penny broke up late-third season and in the season finale Penny started dating again, only to find herself unable to go back to stupid guys after dating Leonard (a physicist). Coming home drunk and depressed she took Leonard to bed, which he misinterpreted as Penny wanting to get back together. She was very embarrassed because that was not the intention (she gets very loose when she drinks) and Leonard was upset over being used for sex.
- Castle and his second ex-wife briefly remembered why they got married and spent the summer in the Hamptons together - which reminded them why they got divorced.
- He also has sex with his first ex-wife (Alexis's mother) about twice a year. They realize they're not right for each other, but the sex is too intense to avoid.
- How I Met Your Mother had an episode revolving around Ted and Robin having sex in order to avoid arguments (they had broken up but had recently become roommates because Robin lost her job). Interestingly enough, their activities did not end because of romantic complications, but because Barney was secretly in love with Robin at the time, and when Ted figured this out (due to Barney's not-so-subtle attempts to stop them from fighting and therefore having sex) he immediately called off his arrangement with Robin and allowed her to believe it was because he was afraid he'd redevelop feelings for her.
- Frasier does it at least once, with his ex Lillith Sternin.
- In one episode, Blossom catches her divorced parents fooling around. They hadn't had sex but may have if they weren't caught.
- Seinfeld did this, with Jerry and Elaine.
- Cougar Town: Jules and Bobby hooked up after having been divorced for a while. Grayson and Andy wrote a song about it, which they called (appropriately), "Sex with Your Ex." It went:
Sex with your ex is really great/but sex with your ex is a big mistake/oh no no/sex with your ex.
- Happened in Pan Am when Bridgett came back, screwed up Dean and Collette's relationship.
- The fourth season of Breaking Bad has Walter having sex with his wife again after they split.
- Raylan Givens in Justified has slept with his ex-wife several times, even though she's now married to another man. They briefly get back together but she soon realizes that he has not really changed and they will never work out.
- Bones: Booth has had a couple of "one time only" sleepovers with his ex-girlfriend, the mother of his son. Similarly Bones herself slept with her former boyfriend (and thesis supervisor) when he came into town.
- Parenthood - Crosby and Jasmine end up in bed together after discussing (over copious amounts of wine) the heartbreak they both felt trying to explain to their son, Jabar, that they wouldn't be getting married.
- In That '70s Show episode "The Relapse" after her mother leaves, Donna is distraught and ends up having sex with her ex-boyfriend, Eric. Eric believes that this means that they're back together, and is quite upset when he learns that it doesn't.
- Hou$e of Lie$ opens with Marty regretting a night spent with his ex-wife. Doesn't stop him from doing it again in other episodes.
- Every. Single. Time. Zoe shows up on Lie to Me, she and Cal get busy.
- The pros and cons are discussed often on Sex and the City. Carrie, Samantha and Miranda all hook up with ex-boyfriends, to varying degrees of success.
Samantha: (while discussing whether or not Carrie should have one last hook-up with Big before he leaves New York) Fuck you once, shame on you. Fuck you twice, shame on me.
- In Miranda's case, she hooks up with Steve after their first break-up which leads to them re-kindling their relationship, and again after their second break-up when Steve is diagnosed with testicular cancer, which leads to Miranda falling pregnant in spite of considerable odds.
- Samantha does this twice with her womanizing ex Richard.
- Mad Men: Betty and Don Season 6 Episode 9 "The Better Half."
- Happened a lot between House and Cuddy. They had a Vicious Cycle of being an Official Couple, breaking up, sleeping together, being friends with benefits, deciding to start dating again, ad nauseum until finally deciding they were Better as Friends.
- Also with Taub and his ex-wife.
- Interesting variation on Star Trek: Deep Space Nine: Worf was married to Jadzia Dax, Dax being a symbiont passed between hosts. Jadzia dies and Dax is placed in Ezri. When Worf sleeps with Ezri, it's primarily him trying to be with Jadzia again.
- In Psych this happens between Shawn's divorced parents, and he is traumatized when he walks in on a Primal Scene. They don't get back together, but are still good friends.
- An episode of Grey's Anatomy has a woman get stuck in a compromising position on top of her ex-husband when his new penis ring gets snagged on her IUD. The doctors have to use expensive machinery to help them navigate their way out of the situation. It gets worse when their daughter finds out her mother is in the hospital and walks in. The daughter is extremely upset at her mother cheating on her new husband, not to mention the hours of therapy that she'll have to go through.
- A seventh season episode of Buffy the Vampire Slayer has Xander and Anya sleep together after their break-up. They wonder if it means that they should get back together but decide that it didn't really feel like "getting back together" sex; it felt like "one last time."
- The Affair: Neither Noah or Cole seem to be able to stay away from their exes for good, even if they're in other relationships.
- Third Watch. Jimmy and Kim can't stop sleeping together despite their divorce, which was due to his frequent infidelity. They actually do reconcile by the series end, after he legitimately gets his act together.
- Knots Landing:
- After he sues her for custody of Brian and Olivia in the Season Two episode "A State of Mind", Abby sleeps with her ex-husband Jeff and leads him to believe that they have a chance of reconciling. However, the morning after the night before, she tells him that it was a one-off and he realises that she's manipulating him to drop the suit.
- While dealing with the emotional pressure of Lilimae deliberately running over Chip, a distraught Valene had sex with Gary in the Season Five episode "... And Never Brought to Mind". As a result, their twins Bobby and Betsy were conceived.
- Gary and Valene had sex again in the Season Nine episode "Weak Moment" as Valene was upset about Ben's continued absence.
- Happily Divorced: In the penultimate episode of season 1, Fran and Peter get drunk and sleep together, resulting in a Pregnancy Scare (she wasn't).
- In Suzanne Finnamore's 'Split,' she admits to having sex with her ex in the midst of their messy divorce, even though he's theoretically with The Other Woman (the same one he left Suzanne for) and she claims that sex is The Best. Ever.
- Warned against in E-ROTIC's aptly-titled "Max Don't Have Sex With Your Ex".
- The subject of Childish Gambino's "Heartbeat" is the narrator having hooking up with his ex while both of them have moved on to other people, and the emotional dynamics of their relationship.
- In Mary, Mary, Tiffany accuses Bob with having slept with his ex-wife Mary, whom he obviously remains attracted to, though he insists that he's the sort of Nice Guy who just wouldn't do such a thing. What actually happened is that he ran out on her after she gratuitously insulted him when he was trying to talk about his feelings for her.
- In Fahrenheit, Lucas can bed his ex-GF Tiffany when she comes to pick up the last bits of her stuff from his apartment mid-game, complete with an interactive sex scene (that was eventually cut from the American release).
- Silent Hill: Shattered Memories: Harry is talked into having sex with Dahlia (who claims to be his wife, and that they've done it plenty of times before). Of course, given The Reveal, it's doubtful that this has ever actually happened.
- Sandra on the Rocks: Domenico's reaction to finding out about Sandra's mo-cap session with Dark Matter games was to call it foolish and demand she cancel it. Except his ex wasn't about to let that happen. One shouting match and a crapload of Belligerent Sexual Tension later, and... cue Sexy Discretion Shot.
- Sam & Mickey had Barbie and Ken break up some time before the events of their first video, but begin an affair in "New Year's Eve". Barbie claims in The Real Housewives of Toys 'R' Us episode #3 that they had to end this affair after the events of "Sex Tape", in which Barbie finally told Ken's girlfriend Yasmin about it. After that confession, Yasmin revealed that she already knew about the affair, removing any enjoyment Barbie got out of trying to keep it a secret.
- One example of this trope with a happy ending is in the Futurama episode "Bendless Love". When Bender gets a job as a "scab" in a factory that is experiencing a worker's strike, he finds his not-so-evil twin Flexo working there too, and also a pretty female robot named Anglelyne who he develops a crush on. When Bender finds out that Anglelyne is Flexo's ex-wife (but still apparently has feelings for him), he decides to see just how far the feelings go, disguising himself as Flexo (easy to do, needing only a small fake beard) and taking Anglelyne out for a night on the town. Unfortunately, this does indeed make Anglelyne remember how much she loved Flexo — but even more unfortunately, this gets the real Flexo in trouble, as the Robot Mafia - who is supporting the strikers - drops an unbendable girder on Flexo to punish him for flaunting his success. Bender starts to feel sympathy for both of them, and he decides to try bend the girder off of Flexo ("Well, I don't know anything about lifting, so we don't have many options here!") and actually succeeds, after which Anglelyne and Flexo apparently make love right there, with Bender still in the room.