The End of the Affair by Graham Greene
The tortured love affair between novelist Maurice Bendrix and Sarah, the wife of a civil servant, reaches its height during the Blitz. Then, without any explanation, Sarah breaks off the relationship. Two years later, his jealousy and grief reawakened by a chance encounter, Bendrix hires a private detective to follow Sarah. As his love turns into obsession, Bendrix begins to question everything he has ever believed in. The End of the Affair is perhaps Greene's most personal and intense novel.