First you have to decide what is more important, your relationship or sex. As a recovering sex addict I have had to make that choice. Believe it or not sex is a choice. Check into Sex Addicts Anonymous. It's a great source of information and help. I would suggest that you not get married until you work this out. It would only make matters worse. By experience, I would suggest that you not cheat. If you have to have sex with someone else break it off with you fiance. It is only fair.