Some men will, some won't, it's not good to paint all men with the same brush.
I'm not seeing how you can be faithful and cheat. Those are pretty black and white words. On the other hand, your first question was can a good man still cheat? I think that is a possibility. Some men are just not ment to be in monogomous relationships, but they might be a great friend, or lifesaving doctor, and a good man in all other ways. Just don't marry him. :)
A good man who is 100% faithful won't. The question is contradictory.
If you have a good man (or woman) and treat them right, would they want to?
I can't speak for any other person who's been in a relationship, but I have had opportunities to cheat when I've been in a relationship and never considered it for a second. It wasn't that I had to think, this would be great but no. If I had to think that I would have been in the wrong relationship. I have been in two great relationships and it was like wearing blinkers.
Being polyamorous, I trust neither my partners nor myself in a marriage.