This film does come close to the original description in the post, and its entire vibe seems to match what the outline in the post suggests.

However, it´s not a harp that the blonde longhair "strokes", but a cello she is fingering and bowing. Besides the woman coming up from behind not only strokes and brushes the cello player´s hair, but she seems to have some definitely sexual plans with the musician right from the start. And there is a third woman on the sofa who soon seems to get a little aroused, too.

A nice film. But were you really searching for something so explicit, at least in 1980´s terms?