A Severed Head (1971)

Antonia Lynch-Gibbon, wife of upper-crust wine dealer Martin, falls in love with her husband's best friend, noted psychiatrist Palmer Anderson. While both Palmer and Antonia would like to remain in Martin's life, he has some secrets of his own — namely, a mistress called Georgie, whom his womanizing brother also desires. All the while, Palmer's sister Honor seems to know everyone's business.