Whistler by Ann Patchett
Daphne and her husband Jonathon are walking through the Metropolitan Museum in NYC when he notices an older gentleman who seems to be following them. It turns out to be Eddie, who was Daphne's stepfather till she was 9 years old, when her mother decided to abruptly evict him from their lives. Daphne and her sister were crazy about Eddie as kids, so Daphne is happy when Eddie wants to resume their relationship. Part of the story is told in flashbacks of a traumatic event that happened to Eddie and Daphne when she was a child-and she had to save Eddie's life. Whistler, the horse pictured on the cover, ties into that event. It's a sweet story of the enduring love between (step)parent and child.