The Constant Nymph (1943)

Fourteen-year-old Tessa (Joan Fontaine) is hopelessly in love with handsome composer Lewis Dodd (Charles Boyer), a family friend. Lewis adores Tessa, but has never shown any romantic feelings toward her. When Tessa's father (Montagu Love) dies, Lewis contacts her late mother's wealthy family so they'll take care of Tessa and her sisters. Lewis becomes taken with Tessa's haughty cousin Florence (Alexis Smith) and the two soon marry and head off for Florence's estate in England. Meanwhile, Florence sends Tessa and her sister Paula (Joyce Reynolds) off to finishing school. The girls run away from school and Tessa moves in with Florence and Lewis. Florence soon becomes consumed with jealousy over the bond between her husband and Tessa.