I'm not going to tell my friend that he could be cheated on
Why wouldn't you tell him about this?
Because I feel betrayed by him. He can't be trusted with his feelings
It's wrong to not talk to your friend about something bad that might happen to his life. If he's your real friend then you should go ahead and tell him.
It's not my place to tell him or get involved. All I care about is getting him riled up about this stuff and if he leaves her then that's great for the both of us.
You don't seem like a good friend if you do this. You should just tell him your concerns not only about the cheating but why you are upset with him.