I Would find this massively hurtful and I think I'd struggle to forgive it actually.In a normal break up then maybe at a push but if he had assaulted you I can't understand the mentality of socialising with him.They can see the kids when they are with you cant they?
Yes I can identify with all of your post almost word for word!It's very hurtful and frustrating.True,you can't stop them socialising with him but he shouldn't be taking your place at family gatherings.I also have a fraught relationship with my DM,it's never been great but is virtually non existent now.I keep contact to a minimum and leave her to it,it had to be done for the sake of my own sanity,however I do miss spending time with my DF.
So Christmas day my brother wouldn't spend with us and the DC as he was spending it with my mother. Boxing day was 'their' Christmas day, long with ex-h and the DC.
My parents aren't together, my dad is great and spends lots of time with us.
My mother and DP don't get on. DP and I had an emotional affair while I was still married to ex. Ex had a drink problem and things weren't great at home, it's a long story. He punched me when he found out. My mother has never spoken to DP and DP doesn't like her because of how she's treated me.
It may feel disloyal but he is the father of their relatives and if they get on with him and like his company then why shouldn't they spend time with him.
He punched you when he found out that you have been cheating (EA is cheating), while that's not OK I doubt its an uncommon reaction from either gender TBH.
Does he still have a drinking problem? If not your family may be questioning whether he had one at all but they're probably blaming you for the break up of the marriage because of the cheating and may even feel sorry for him.
Oh the doing it for the children's sake,that's my DM's line too! I'm guessing that she sees your DP as the OM and responsible for the break-up of your marriage hence why she isn't friendly or welcoming to him.