Distortions (1987)

'Distortions' is kind of a murder mystery. When Amy learns that her husband died in an explosion when his car when off a cliff, she suddenly finds herself being watched by a strange man (who makes no effort to hide himself).

The movie opens intercutting scenes of a man with a mustache getting dressed while a woman is in his bed, and that same man getting dressed while a man is in his bed. We see him go cruising, and he picks up a gigolo with a mustache.

A real heart-thumper, even 13 years after its release! I saw this when it first came out, and again on video-- same effect.