I am just gonna throw this out there. It might not be jealousy. They may well have been trying to protect him. While misplaced, its not a bad thing. Sounds like it was handled improperly though. If the wounds can be healed, they could end up a very tight knit group of friends. I would rather have friends like that than what I got stuck with in the past.
I was with a woman 7 years. AFTER we broke up everyone told me how bad she was for me, what a rotten woman she was (I met her when I was 17 and she was 23). This is family and friends. None of them bothered to try and approach me during the relationship. I'll take his friends over my ex-friends anyday.