:hug:its difficult to answer not knowing you but i do know about the damage that kind of controlling relationship can do - so firstly if you had not got out when you did think how much damage could staying have done to your son - your ex could have extended that behavior towards him as well and even if he had not directly done that your son would have learned that behavior and your acceptance of it and think its OK - maybe carried it forward into his future relationships as well -so in my opinion you did the best for your son by leaving.
Secondly there were two adults involved - you were not solely responsible for ensuring the relationship between them continued - your ex could have made the efforts that you now feel was all up to you to make but it was up to him as well.
From my experience of people who behaves like that, it is possible he tried to use contact with your son initially to continue to control you and stopped making any effort or initiative to see him when it didn't work the way he wanted.
Those family events may have been much less happy occasions for your son to look back on if your ex was there and creating family tensions that at best your son could have been aware of and stressed by , and at worst could have ended up in a brawl ruining it all .
Also any invitation to attend them by you might have been seen by your ex as a sign you wanted him back - in his mind, because there is often a focus just on self that goes along with this kind of behaviour, any invitation you made on behalf of your son could be seen by him as something more than that.
That doesn't take away from your grief and of course no one wants to see their child suffer it, but i wonder whether it is not that alone but your grief too - not for what was, but for what could have been if he had behaved differently - and it might seem that it is so much later to reflect on that now - you would have done that grieving for what could have been when you left, but maybe this has caused you to re-visit those emotions again now.
He was your sons father and that doesnt change and at some point you had a good relationship with him - sadly his behavior blew the relationship and familly life that could have come from that out of the water -that wasnt your fault and i still think what you did was not only very brave but the best thing for both you and your son.
I have no idea about how much your son knows about any of this but of course he will grieve his father if not for what was, but for what could have been -he may even be blaming himself for not initiating contact as an adult when he could have done.
I had only met my dad 3 times before he died and what i grieved for was the future, the time he could have spent with his grandchildren the time i could have spent getting to know him - they split for a very different reason - but i did not in any way start to blame my mum i knew why things had been as they were and was the same age as your son at the time.It isnt your fault and i am sure he understands that with you as i did with mine and isnt just saying it because he loves you, but if he does have questions over the coming months answer them honestly and if he doesn't yet know why you left look for a way to answer as gently as you can -maybe along the lines of "your dad did these things i dont know why he did but maybe it was because he had a mental health issue and couldn't manage it or it was never diagnosed, or maybe because he had grown up in a house where this happened and didn't know and couldn't understand it was not acceptable behavior, but i could not live like that any longer and i didnt want you too be living in those circumstances either so i had to make the decisions i did."