Disbelief,

It cannot hurt to try. You never know what is another person's heart. If she is involved in an affair, then the chances that changing yourself will change her mind are not high. But if she is not in an affair, it could be that just by becoming a better person, you will attract her back. The key word there is attract. You won't get her back by begging, crying, or trying to make her feel guilty. She is trying to have a better life. Can she do that with you? Can you show her how life with you can be better than it was? Those are the kind of things that might make a difference.