My Mother's Friend (1975)

A woman, who has just separated from her husband, comes to stay at the villa of the friend. The friend is away (and throughout the whole movie only appears as a voice on the phone), but the woman's goofy son (who looks like he just escaped from the Monkees) is staying there too. The son falls for her, not surprisingly since she always dresses in skimpy miniskirts or bikinis, and rarely closes the door when she is changing clothes or showering.

Unfortunately the movie My Mother's Friend is not yet available on HBO Max.