Illicit Affairs(1989)

This underrated little film is an adult twist on the old film classic "A Letter to Three Wives. " Victoria Paris and hubby Robert Bullock are vacationing with Sharon Kane and her husband Randy West, and Jon Dough and Aja. While getting a tan, Paris finds a letter she believes was written by one of the husbands promising to run off with another woman. That sets Paris wondering which of the insecure relationships is about to crack.