Valse à trois (1974)

Paul, a biochemist with a quiet life, meets a very young hitchhiker named Hélène. She embodies bohemianism, love, and fantasy... everything he lost after marrying Claire, a beautiful, sophisticated, bourgeois blonde, thirteen years earlier. Paul and Hélène become lovers. He sets her up in a small room in a seedy motel. Naturally, this reaches Claire. And to make matters worse, she also discovers that Hélène is pregnant by her husband. Wanting to avoid scandal, but also because she has had children and realizes that Hélène will not be able to decently take care of hers in this miserable room, she invites him to come and stay with her. A complex relationship, somewhere between fascination and repulsion, is born between the two women.