Try to figure out why you were so weak, so easily involved in an affair. Try to improve yourself, find out what you want out of life; we call that GAL (get a life) around here.
Have you apologized to your wife? Really apologized? Not for the sake of having her forgive you, but to accept responsibility for your actions? Try to put yourself in her shoes; the pain of betrayal is very harsh.
You need to accept responsibility for your actions, and be the man that you should have been for the last 15 years. Perhaps if she sees some substantial changes in you, she might soften her heart. I wouldn't expect it, for some women, infidelity is a dealbreaker.
Your situation really isn't that different than most who are here. Whether you cheated on your spouse, got addicted to computer games, neglected her, were a control freak, etc. you've got a spouse who has decided to say adios to more pain. Maybe look at it like that and use the examples of others who have pioneered some of the best strategies for coping with losing your spouse.
