I'm going to tell my friend he's being cheated on with his other friend, I think. Is that okay?
Oh gee, I don' t know if that is okay. Why do you want to hurt him?
I do not want to hurt him, I just want him to know the truth.
If your friend is being cheated on, it is good for him to know sooner rather than later. It would prevent him from thinking the relationship is fine, when it is not in reality.
Can't I just tell him after the relationship is over? Now I am getting nervous. I didn't realize he might feel hurt so much.
But you need to tell him out of sheer honesty, he will need to know, Then he can move on and be happier with someone else. You wouldn't want to be in a stuck relationship with the other person cheating on you would you?