Please don't list this on a work's page as a trope. Examples can go on the work's YMMV tab.
Love in Hollywood means you'd do anything for your sweetie. When you're the more famous/talented one, you get to feel good about lifting your partner up to your level. But you're also obliged to step down to their level when they ask. So you grit your teeth and star in their off-off-off-Broadway show, or jump on stage during their concert, or cheer when the camera pans to you in the stands during their basketball game. Julia Roberts dated Benjamin Bratt for a few years. Here's the proof.
For whatever reason, when married couples (or even just couples who are known for being together) make a movie, it rarely works. Who knows why? In some cases, it's public backlash against the couple. Sometimes the couple's Real Life chemistry just doesn't show up on-screen (or it does, and it becomes somewhat unsettling when you realize you're watching an actual couple during a love scene). Sometimes, it's just a vanity project with no real direction. In any case, even though Couple Bombs have a track record of not succeeding, they somehow still get made anyway.
Subtrope of Real-Life Relative. Might be related to Creator Couple if the Love Makes You Uncreative trope is factored in. Should not be confused with Battle Couple.
Gigli is probably the most notorious example. Even though Jennifer Lopez and Ben Affleck weren't married at the time, they were the hot couple, and the movie was significantly rewritten during production to capitalize on their relationship. In a twist which surprised no one, Bennifer called it quits shortly after the movie bombed.
Swept Away, sort of. It starred Madonna and was directed by Guy Ritchie, and was almost universally panned as being terrible, and led to Madonna's declaration that she would never act again. You promise?
The original script probably didn't set the world on fire, but the decision to include the couple was a fatal one, on multiple levels. Shooting began in Hong Kong and problems soon arose: the exposure produced by such a hot tabloid couple served as catnip to Chinese gangsters, who sabotaged equipment and even extorted money from Madonna and Penn before they'd allow them back on set. Penn, like clockwork, went berserk every time a paparazzo snapped a picture of him, culminating in an assault charge. Eventually Penn and Madonna stopped cooperating altogether, causing the budget to balloon as directors and actors were replaced on Penn's decree, and the couple were labeled as poison.
El Cantante (Marc Anthony and Jennifer Lopez).
Dirty Love, written by and starring Jenny McCarthy and directed by her then husband John Mallory Asher. They divorced shortly before it went down in flames.
In 1959, Audrey Hepburn starred in Green Mansions, directed by her then-husband Mel Ferrer. It was one of the least successful movies of her career.
In The X-Files, Mulder had a one-night stand with the actor's then-partner. The crew later noted that it was to the detriment of the love scene, because there was just no tension between them.
Peter Sellers had couple bombs with his second and fourth wives: The Bobo with Britt Ekland (they also did After the Fox together, but in that film they play siblings, not lovers) and The Prisoner of Zenda (1979) with Lynne Frederick.
Discussed Trope on Friends. Chandler is worried that his actress girlfriend Kathy is cheating on him with her co-star after seeing their steamy sex scene, but Joey assures him that actors that are actually together have no chemistry with their co-star.
William Daniels and wife Bonnie Bartlett also avert this trope rather spectacularly. They both won Emmys (in the same year) for their work as a married couple on St. Elsewhere. In Boy Meets World, Mr Feeny (Daniels) falls for Dean of Pennbrook Lila Bolander (Bartlett), and it's one of the sweetest arcs in the series.
Al Jolson and Ruby Keeler in Go Into Your Dance (1935). Two Broadway musicals also tried to capitalize on their relationship: Ziegfeld's Show Girl (1929) billed her as Ruby Keeler Jolson and for the first few weeks had Jolson (under contract to a rival producer) singing "Liza" to her from the audience; Hold on to Your Hats (1940) tried to revive the collapsing Jolson-Keeler marriage by having the two appear on stage together, but this backfired during the tryout, with Keeler leaving the production and divorcing Jolson.
Paul Hogan and Linda Kozlowski made the Crocodile Dundee movies together. She divorced her husband to be with Paul after the first one, they were dating during the second one, and by the third they had been married for a decade.
Fibber McGee and Molly on radio were great together.
The two leads in Monsters were dating at the time (and have since married). The director wanted to cast a real-life couple because the chemistry between the two was so important. The film ended up making $4 million on a budget of under $500,000.