Off the beaten trail of long-lasting romantic pairings, but Deborah Harry and Chris Stein of Blondie were a couple for ~13 years. But even after separating they apparently remained good friends to the point where Harry is the godmother to Stein’s two daughters. They have continued to work together more or less steadily to this day, some 42 year after they first met.
Kind of rare to see that kind of post-romantic relationship work so well, particularly in the ego and drama-heavy world of the arts ( and Harry and Stein aside, Blondie was a drama-heavy band ).