The Constant Nymph (1943)

Fourteen-year-old Tessa is hopelessly in love with handsome composer Lewis Dodd, a family friend. Lewis adores Tessa, but has never shown any romantic feelings toward her. When Tessa's father 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 and the two soon marry and head off for Florence's estate in England. Meanwhile, Florence sends Tessa and her sister Paula off to finishing school. The girls run away from school and Tessa moves in with Florence and Louis. Florence soon becomes consumed with jealousy over the bond between her husband and Tessa.