A Touch of Class (1973)

They had the perfect love affair. Until they fell in love.

Steve, a happily married American man living in London meets Vicki, an English divorcée and run off to Marbella for a rollicking week of sex. They then return to London to set up a cozy menage, despite the fact that he loves his wife and children, and now realize that he and Vicki have also fallen in love.