My experience has been opposite - but I say this lightly because 1 - I've only been in one actually serious relationship and 2 - I was something of a man whore in my "younger" days which probably doesn't seem to make a lot of sense but I think it does - to me, anyway.
The only serious relationship I had she told me she couldn't wait for me grow up and be confident (those weren't her exact words but what she needed) and moved on. I wish she had waited until she told me, but I knew (it was an expectation, I guess) that she wouldn't last forever with me and I was just glad for the time she gave me even though it sort of destroyed me in the end.
I'm not sure what it is (well, I have a pretty good idea actually. I don't know if it's fixable) but I just don't seem to be made for relationships. Prior and after that one, I've been with girls but it's always been more of a "friends with benefit" I guess but not? Sometimes it was the type of girl I was dating. If they were in a relationship when we met (yeah, I was and am not perfect) I know they're likely to cheat because that's what I am helping them do but for **** sakes don't check out that other chick... lol I found it rather enduring, I guess, because it made me feel like I was something more then I was.
Anyway, during all that I never hooked up with another girl when I was with any of them. But I knew I was always momentary relief until they got tired of me and I was out the back door. I'm pretty much an all or nothing person so when I'm in, I'm in but I know that I don't have anything to offer, really - so they always ended up cheating, but I couldn't hold it against anyone except that one and I think that's just because I bared a lot of my soul to her and I was scared knowing there was someone out there that knew that much about me. I still miss her and I still feel a lot for her, though we haven't talked in years.
I'm not in a relationship now but there is a girl that just won't get out of my head but I'm at a bit of a stand still because of all that I am and because I've been warned off, so to speak - but I haven't slept with anyone since we started talking - her included - because... I don't know why, actually. I guess the thought makes me feel like ****.
I think the biggest issue people that cheat have is that we don't stop to realize that the person you started dating most likely isn't the same person you are now, especially in long term relationships. We never stop growing and learning and we change all the time. Accepting the good and the bad of someone you 'love' is something we need to teach ourselves and I think if we can't learn to readjust to learn to love each different aspect of that person we are with it'll never work and you can't expect someone to always stay the same.
And if it's just too much effort to learn to re-love then it's probably time to let them go - just no one really ever has enough balls to do this BEFORE the cheating comes into play.
Anyway, that's just what I think but I have a rather slim repertoire to back that up with so... I could be right out to lunch, who knows.