Sweet William (1980)

William McClusky (Sam Waterston) is a dashing and eccentric Scotsman whose charms rapidly overwhelm the sweet and naive Ann Walton (Jenny Agutter), but she nearly as quickly begins to comprehend that her new beau is anything but a one-woman man. In addition to his two ex-wives, with whom he remains remarkably close, William exhibits a disturbing attraction for nearly any female who crosses his path -- Ann's friends among them.

Unfortunately the movie Sweet William is not yet available on HBO Max.