I wonder if there wasnt something between your friend and your brother? This seems like a lot of trouble over something somebody only said, not something that was done. Boys get up to a LOT of trouble. So do girls, but boys brood more, i think

If your brother wants to make a scene at your daughters sweet 16, that kinda says to me that he is expressing anger at his own innocence being violated? And having your friend there - as if nothing happened, when maybe something more than you realize did indeed happen - is triggering him to lash out?

Maybe talk to him, maybe see a family counselor with him to talk about it? Idk what to do if it turns out there was contact between him and your friend. Im glad to hear your brother is considering therapy.

Boy it never rains but it pours, huh?