DEAR ANNIE: I have been married for 15 years. A little over a year ago, I started having an affair with an ex-girlfriend. The affair ended a month ago. It is over and done with. I am not sure if I should tell my wife about it or just keep it a secret. I feel that if I tell her, nothing good would come from it, other than being truthful. However, I see it destroying the trust she has in me. I can’t think of a good reason to tell her. What should I do? — A Cheater in Upstate NY DEAR CHEATER: Ask yourself what your intentions are in confessing. Are you doing it to relieve yourself of guilty feel…