An Elephant Can Be Extremely Deceptive (1976)

French comedy about Etienne (Jean Rochefort), a happily married man and a good father. His friends all have secret affairs and/or cheat on their wives. One morning, Etienne sees a woman in red passing by his car. He falls instantly in love with her and tries everything to get to know her better. Of course, this must be kept a secret from his wife.