OP, from what I have read, you were in a relationship with him-and it was awful. He talked you into giving it another go -it was also awful. Imho, giving it another (and another and another) chance isn't you being bad; he manipulated you into it. It was still awful and this is all based on his behavior (all of this manipulation perhaps?). You broke up because you rightly refused to be invisible to his psychological needs.
You have moved on with relationships, yet you still have an emotional connection with him. And apparently he does with you as well. In both cases imho, these connections are not in a good way. He has some level of hatred for you (imho, because he did not get his way) (yes, hate is a form of connection).
Your connection is more tricky because it is the damage that a narcissist can do manifesting itself. Very subtle, but he has you believing that the break up was your fault, that any feeling he has had associated with the breakup is also your fault (understand that you are not in control of his feelings which goes hand in hand with not being responsible for his happiness). Narcissists, imho and experience, will not (perhaps can not as their brains may be wired differently) take responsibility for their hurtful, negative, degrading, uncivil, (the whole menu of how they may administer Death By Ten Thousand Cuts) behavior. He is using the group as he needs to for the purpose of shoring up his archangel persona...without the audience, (or horse stable full of individuals he uses for supply), he is nothing.
The group is under his spell. You know the facade is fake and can spoil everything. That is why he demonstrates the rudeness (hatred), imho.
Please, work on achieving a position of complete emotional detachment from him. No, not just like he doesn't exist- he obviously does exist. More like he exists as a stranger on the street...You just are not connected to that person. You are no longer associated with that person so he does not rate any brain space. (Hopefully someone will come along and explain this better!
)
Do not email him. That is a connection, and I have no doubt that he would make hay out of it no matter what you wrote.
Do not smirk at him. Without the narcissistic element, this would be perfect. But any reaction from you will be entertainment fodder because you are not dealing with a normal person or normal social intelligence ground rules.
It may be best to take a break from the group. In time, one by one, folks may seek you out to confirm their experience with him (and decide to spend time with you instead). His stable will dwindle...perhaps over a period of years. You do not need to witness it, no shadenfraude. Be glad you are out of the relationship. Pity the lady who is with him now as he will not change...Well, only change to become worse.
Sorry the price for getting out of that relationship is so high, even after years time. But your mental health was/is at stake and you did nothing wrong, imho.