Well it seems that both are of you are confused. If you can be without each other than why are you married to someone else? I am not trying to be mean but have you asked yourself about the way you feel about your spouse? THink of it this way, no matter how much you say you love each of them, by being with both neither of them has all of you. No matter how hard we try we cannot give ourselves completely to two people. Someone always loses out.
Also just think about how you would want to be treated if it were him cheating. Would you want him to continue sneaking around behind your back or would you want him to be honest? If you really want to keep your marriage then you will let your boyfriend go.
Many people cheat because they are not getting something at home. So maybe your problem could be to re-evaluate your marriage and see if there is anything you feel that your spouse is not giving you. THis could be something emotional or sexual. If there is something then maybe you could talk to your spouse or seek a counselor to see if you can turn things around. As far as being friends with the other person, maybe that isn't such a good idea if you are as addicted to him as you say you are. This doesn't mean that you have to cut all ties to him but things like being alone and having long intimate conversations on the phone are not such a good idea. Tell him both of you should refocus your energies on the marriages that neither one of you want to destroy, he should understand that.
Good luck!