have you considered talking to a therapist to help figure out what drove you to cheat in the first place? maybe once you know the answer to that you'll have a better idea of whether couples therapy might help your marriage.

personally, i don't think telling your wife is the answer. that would relieve you of your guilt, but it would stir up a lot of awful things for her. i think you'd be better served correcting your behavior and trying to be a better husband.