The Life and Loves of a She-Devil (1986)

Ruth has everything. A large, warty body, a standard house in the suburbs, two whiney children, a dog, a cat and a guinea pig. She also has Bobbo, her unfaithful accountant husband who resents her very existence. Bobbo wants, and is wanted by, Mary Fisher. Mary Fisher lives in a lighthouse by the sea and writes about love. When Bobbo leaves Ruth for the novelist, she decides that Mary Fisher doesn't know the first thing about love. Ruth intends to teach her.