"is wanting to cheat as wrong as cheating?"
Wanting to cheat is as bad as cheating, but actually acting on it is worse. Don't ask how that works, because I don't feel like explaining female logic right now.
"is thinking cheating is wrong and doing it anyways the same as thinking it's fine but not cheating?"
If you do something even though you know it's wrong, I don't see why anyone would want to be with you. At least the latter has enough common sense to NOT go looking for someone else.