For the last five years of my second marriage, we slept in separate rooms. We agreed that we would not ask and not tell, but if either of us DID ask, we'd be honest. During that time, I had what I would call an emotional relationship with a married co-worker. She and I never acted on it, other than spending hours talking, and sharing our most intimate feelings. I always had pangs of guilt, but chose to ignore them, as did she. We talked about that, too. Ultimately, we went our separate ways, and neither of us was hurt, nor were our marriages, but we could have easily created a great deal of irreversible damage in our lives, had we not broken things off. I know that does not answer your question, but it is simply food for thought.
Also, I would add - about cheating - Anything that you feel you need to keep secret from you spouse or family (even if it just masturbating in the corner to some fantasy picture or porn) I believe constitutes cheating. I think that if there are guilt feelings associated, regardless of what the action is, it is probably cheating, on some level. Regardless of what kind of cheating someone is doing, someone always winds up getting hurt.
