La Femme fatale (1946)

Fanny Le Doublond has a lover, Jean, and her husband is beginning to have suspicion. To calm him down she makes him believe that Jean dies of love for another woman and wants to commit suicide if his love is not returned. The two accomplices select a young creature named Claire Coussol for the (unwitting role)of the "beloved". As for Jean, he plays the suicidal man to perfection. But what the two lovers had not planned at all is that Claire, deeply moved by Jean's "act of desperation", starts growing fond of him.