The "I'll never see my friends again" argument is pretty pathetic. The situation is that you'd like him, and he should also think this way, to see all of his friends, with the exception of this one. You are not stopping him seeing his friends, just that one.
So, he misses a party, so what ! He may miss a few other events too, so what ?
Why can't your DH take control of the situation and organise his own social events, obviously not inviting the one person who insulted you. That way he doesn't miss out. Surely, even if they don't want "to get involved", the other friends should still be able to understand and respect his stance in excluding / not wanting to socialise with this jerk any longer ??
I'd certainly feel very very hurt and betrayed if someone insulted me and my DP chatted to them like nothing happened. Do you feel able to tell us what happened ?