When Love Is Lust (1974) on Netflix

A young girl, Erminia (Agostina Belli) marries a handsome and successful but brutish local butcher, Antonio (Gianni Macchia) at the behest of her countess stepmother, Giulia (Françoise Prévost). The new wife turns out to be frigid on their wedding night, and the couple have a big fight. She leaves the town to stay with her older, married sister Angela (Ewa Aulin), and gets involved with her sister's jaded swinger friends. The husband consoles himself by picking up prostitutes and carrying on with a sexy, voluptuous wealthy widow neighbor (Femi Benussi)right in his new mother-in-law's villa. For some reason the mother-in-law considers this a turn-on and becomes sexually drawn to her loutish son-in-law.