Les félines (1972)

Oliver is married to Maude, who runs a high class fashion shop and has a mistress, Claire, who is her customer. Maude decides to let him have his fun as long as she can control them. She brings Florence, a very attractive 18 year old, to live with them and to seduce Oliver. The plan works, and he soon gives up his mistress for the younger girl. But as the the time passes, she not only captivates and controls Oliver, but Maude as well.