Boyish (1957)

Monique is an ingenue, a clueless girl who believes in true love, for her fiancé is a handsome man, and at the time (early 20th century), marriage is the only thing a decent girl must long for. When she discovers that her future husband has a lover, she rebels against her bourgeois family and their money math; she will live a wild, free life--she will live like a man. Soon she becomes the toast of the Gai Paris, sleeping with all the men--and even a woman.