In my experience one of four things happen. Even though someone might genuinely believe they have ended the affair because they realize how much more important their marriage is, this is not sufficient to really end it emotionally. There has to be a real process of acknowledging the loss in order to be completely free to move on. This is something most people who are leaving an affair need to do on their own, not with their spouse. The discoverer of the affair cannot stand the thought of reentering the sexual relationship.