I once saw what I think was an English movie from the late 60s, maybe early 70s.
It was about a middle class couple. He was a bank clerk I think in a striped suit and a bowler hat.
She fell in love with the milkman, who secretly started living in their basement and the woman and milkman lived a wild life with parties and drugs without her husband knowing about it. After a while she marries the milkman and the milkman moves upstairs and starts living the dull life to pay the bills. Her ex-husband secretly moves into the basement and starts to do all the things with the woman he couldn't do when he was still paying the mortgage.

I would love to see this movie again, but I can't seem to find out anything about it. I can't remember the title nor any of the actors. It might have been a B&W movie, even that I can't remember.