Age of Innocence by Edith Wharton
Set in New York's High Society, Age of Innocence is The story of a young man trying to follow the rules of society against his vague discomfort with them. Newland Archer is a young lawyer engaged to the proper young lady, May Welland. Everything is on tract until May's cousin returns to New York.
Countess Ellen Olenska has left her husband amid scandal and returned to her family. But in the late 19th century divorce is a scandal. So Newland is drawn into the family's efforts to persuade Ellen to return to her husband. And Newland finds himself attracted to her and begins to question the path he is taking.