Aye, I think he's way over-reacting. Yes, it was a betrayal, and dealing with betrayal is tough, but it was 17 years ago, and Matt is still his son in every meaningful way, and Julia is still his wife and the mother of his son, and Christian is still his friend, and all of them have been so for the last 17 years.
He needs to suck it up. And it appears that he is.