I'm going to tell my best friend how it is
Why tell it like it is to a friend?
He doesn't get to be like that with me, I'm only doing this for him
Your friend has a right to know what sort of situation they are in, even if it's negative. You may not be friends anymore after the situation, but you will still retain some degree of respect for telling the truth.
I'm doing it because I want to see if he is really a friend and see if he will respect me or not as a friend.
That's a bit roundabout. Just tell him the situation and ask the truth from him.