Death of a Nymphette(1967)

Recently divorced, Robert Allan meets Peggy at a party and she soon becomes his mistress. The affair ends, however, when Robert discovers that Peggy is a nymphomaniac. Robert next has an affair with Gloria, but it also ends when he discovers that Gloria, unresponsive with men, is a lesbian. Robert finds happiness at last with Frenchy, but their idyl is shattered when two men break into the apartment, overcome Robert and assault and murder Frenchy. Her death drives Robert insane.