All you got to do is ask the guy. If he did not do it he will be grateful that you told him so he can clear it up. If he is cheating and he gets mad at you that's ok. You don't want to be affiliated with a cheater anyway. I guess I don't see the issue. ( sorry but these type people get under my skin. The ones that talk behind your back and cheaters)
Kevin if people know he is cheating and aren't taking steps to make it stop they are just as guilty. It sucks if he is but someone has to address the situation. It's not fair to those he cheating against and like you said its killing his rep or has already killed it.