Yes, I think you were too good at raising your son "evenly" so he has no clue how you feel or what his father did specifically, etc. (since you got divorced when he was so small and all the interactions took place in your home and were "controlled" by you). Since the other players don't have a clue how bad it actually got it being "before their time," I would either keep it that way and see your son when/how it's easy for him (and sounds like he's letting his girlfriend dictate that which is even further removed) and keep pretending or decline the invitations to be with your abusive ex- now that you don't need to. But twenty years and other people's relationships with your ex- stand in the way of it being "the same" or understandable by anyone coming along "now."