I saw this movie nearly 20 years ago as part of a Channel 4 season of dramas & recall being impressed by BA Robertsons' acting ability, and Judi Trotts' musical work. I actually tape recorded the songs late into the film, as I was really enjoying them! (sadly I only have 3 and I cannot find it on sale or in any private collections, which saddens me). I was 15.
There is a "Living apart together" on sale but it's a Dutch adult movie starring Sylvia Kristel, not a romantic musical comedy.
A realistic tale of, as I recall, a couple called Richey & Amy (Barbara Kellerman) who split up due to differences in character. Richey is a very talented, eccentric, but overall irresponsible husband, who you can't help but love. Amy is a romantic, beautiful, all-woman "English rose".
Richey has an affair with Judi Trotts' character, experiencing his "grass on the other side" and the two indulge in a "Baker Dr. Who/ Romana II" mad week, involving a number of well-written songs (created for the movie by Robertson & utilising the talents of himself, Trott, and, very memorably, the incredible Carol Kenyon, known for her work on the Heaven 17 track "Temptation".
The movie does have a happy ending, and gave this 15 year old a good look at modern relationships. A film I have wanted for AGES!
Moresoe as it features a very young Peter Capaldi!