Post 47.
Melissa McCarthy and Ben Falcone (he was “Air Marshall Jon” in Bridesmaids) have been married since 2005.
I seem to remember their real relationship actually occurred during the first year or so of shooting the series, before their on-screen one did. And their real one had ended by the time their pretend one started. Knowing this and watching those later episodes concerning them being together on one hand gives me great respect for what it takes to be a professional actor. But at the same time it creeps me out a little, knowing that they probably lived thru most of the stuff for real together that they were now pretending to go thru as actors together (a relationship starting, flourishing, then breaking up and ending)…
No one has mentioned Sonny and Cher?
They started dating in the summer (2004) before the series premiered, during the production of the early episodes. They called off their engagement in August 2007. In the season 5 finale (May 2009), Cameron and Chase had their wedding. Awkward. They didn’t stay together long in the show. Divorce papers show up in episode 17 of season 6. Morrison had not appeared in 8 episodes earlier that season.
There was plenty of time for the writers to take the Cameron/Chase thing in a different direction but they didn’t.
In Charlie’s Angels, Tom Green and Drew Barrymore were sort of a couple as they were in real life.
Presley was quoted as saying, “every leading lady except one.” Both Ann-Margret and Mary Tyler Moore claimed they were the “one.”
From Sherlock, Martin Freeman (Dr Watson) and Amanda Abbington (Mary Morstan) have been partners since about 2000 according to Wiki.
To keep it all in the family on Sherlock, Benedict Cumberbatch’s real-life parents appear in the series as Sherlock’s parents. So they are a two-fer - married couple playing a married couple who are also playing roles as parents to someone they are real life parents to.
Not sure if this has been posted already.
In the NBC comedy Undateable, the characters Leslie and Mike are dating. In real life, the actors playing them, Bianca Kajlich and Mike Catherwood, are married. 
Now broken up, but Banderas and Griffith. Did either her or her mother ever work with Don Johnson?
A quick look shows that Johnson supposedly started dating Griffith when he was working on Harrad Experiment with her mother. This says she was 14.
Griffith and Johnson worked together in Paradise which I don’t remember at all.
Ronald Reagan and Jane Wyman, and then Ronald Reagan and Nancy Davis.
Cruise and Kidman were also in “Days of Thunder”. Not sure if it counts because I think that is where they met and I don’t know when the relationship started. Similar comment would apply to the “Once” stars.
I wouldn’t count anyone appearing as themselves - i.e. Sonny and Cher - versus playing a role.
ETA: Any relationships that started on a set last? Since all marriages end, either by death or divorce, pick an arbitrary number of five years.
Travolta-Preston
Hanks-Wilson
Fox-Pollan
Benning-Beatty
Jackman-Furness
Ripa-Consuelos
Stiller-Taylor
Gellar-Prinze
Denisof-Hannagan
Affleck-Garner (now done but well over 5 years)
Susan Clark met Alex Karras in 1976 when they costarred in the TV movie, Babe, in which she played the all time greatest ever athlete Babe Didrikson and he played her husband, professional wrestler George Zaharias. They remained married until his death on October 10, 2012.
Couples where the characters’ wives guest starred on their husband’s shows: (so they didn’t meet on the set but got word-of-mouth hires)
John Slattery’s wife played Roger’s first wife on Mad Men
George Wendt’s wife played Vera on Cheers (the Thanksgiving eppy where Diane hits her with the pie.
Sherilyn Fenn guested on 21 Jump Street pairing up with her then-BF, Johnny Depp.
I’m hearing same situation with Jake Mcdorman on Limitless, his GF, Analeigh Tipton is playing…Jake’s character’s girlfriend
----A recently wed couple who met on the set, Amber Stevens and Andrew J West on Greek in 2009. They got hitched a year ago. She played Ashleigh and he played Fischer, the guy who cheated on her. Incidentally, also on Greek, the actor who played Rusty dated the actress playing Rusty’s first girlfriend for awhile. Also, the actress playing Rusty’s sister, Casey, dated the executive producer (Spencer Grammer and Shawn Smith)
Robert Wagner and Jill St. John were a couple when they did a Seinfeld episode years ago. They did a TV movie, Northpole, last year but I’m not sure if they’re still a couple.
Chad Michael Murray and Sophia Bush married and divorced during the course of their starring on One Tree Hill. Their characters were off and on together. Reportedly Paris “worthless trash” Hilton had something to do with it after he worked with her on a movie.
The scene in Orphée en Enfer where Jupiter disguises himself as a fly to seduce Eurydice? In the Opéra nationale de Lyon production, they were humping and grinding so intimately I thought “Only in France…”
After watching, I learned that they were played by Natalie Dessay and Laurent Naouri, who are totally married to each other in their offstage lives. Well, he kind of gave it away how he kissed her at the end; it looked like a real marital kiss instead of a stage kiss.
William Daniels and his wife Bonnie Bartlett on “St. Elsewhere”?