Un Coeur Qui Bat (1991)

Synopsis
In this somewhat unusual romance, the two lovers go to bed with one another first (almost before the films opening credits are done) and then spend the rest of the film getting to know one another, while they carry on with their passionate affair. Malo is married to a very pleasant man, an antique dealer who has provided her with an exquisitely appointed, if unusual, home in the form of a houseboat on the river Seine. They also have a teen-aged son. Yves, the other lover, is also married. While Malo isn't prepared to leave her husband, whom she still loves, she is certainly having a lot of fun with this new man in her life, and they have sex with the frequency and urgency of teenagers. ~ Clarke Fountain, All Movie Guide