Ok, so this rich, single mother of a teenage girl, has a new man in her life, who the daughter doesn’t like or trust.  She thinks he is trying to kill her mother for her money, and keep foiling the ” mishaps” , getting in trouble by her mom and the police.  Determined to catch him, she enlists a teen boy, who she ends up losing her virginity to later, catch the step dad having sex with his lover.  Fast forward, and I think the mother and girl are captured, and the stepdad has been double crossed by his lover, who had a boy friend, when the girl shows the lovers boyfriend a polaroid of the stepdad and the lover ENJOYING their encounter, all he’ll breaks loose.  I’m dying to get a hold of the name of this movie so I can buy it.  We rented it at family video in Springfield Illinois in the late 80s.