Lover (1992)

Marie lives with Antoine, but while he is away she meets Paul, a filmmaker visiting from Canada. Paul is instantly smitten and wants her to marry him. She puts him off by saying that she and Antoine have decided to have a baby. When Antoine returns, he becomes vividly jealous of his girlfriend’s chaste encounter, which provokes her into having an affair with Paul.
Jacques Doillon
Charlotte Gainsbourg, Yvan Attal, Thomas Langmann, Stéphanie Tchou-Cotta, Thierry Maricot
tt0103681