Sibling Rivalry (1990)

Marjorie Turner is suffocating. Her younger sister Jeanine has no ambition, and her 8 year marriage to Harry puts her in constant competition with his family (all doctors), whom he is also competing for the affections of. One day, she snaps while food shopping, and beds a mysterious man, who die during the moment of passion. When she forgets her wallet, a vertical-blinds salesman finds it, and things get complicated from there...