He Is Mine = The Faithful Heart — Patricia Robins

Harriet was very young when her ambitious, unscrupulous mother succeeded in parting her from the impecunious Paul, the medical student Harriet loved. So successfully was Harriet convinced that Paul did not return her deep-felt love, it was not long before she turned, in her loneliness, to the eligible Tony, a charming young man who seemed to adore her and of whom her domineering mother approved. Once married to Tony, it was not long before Harriet found herself fighting against her disillusionment and doing her best to remain loyal to her vows. But by chance Paul comes back into her life when she is most alone and in need of a friend.