@CarriesShoes it’s hard to understand the situation fully but what I think is happening here (and I could be wrong) is that, simply put, there has always been some dysfunction/ unhealthy behaviours within that first family.
When you met him initially, it was either masked (by him deliberately) or it was more subtle / underlying stuff. The fact that you married and the EXW kicked off and caused the subsequent shit show talks to the core dynamic of your relationship between your H and EXW.
A healthy person would have managed it (especially since it happens years into your relationship). A healthy person would have been able to put in appropriate boundaries, say no to certain things and continue to prioritise their current marriage.
This stuff (I think) predates you. And (like many other situations), started to really show up once you were committed/ married to him. He no longer had to make an effort (with you) and he has effectively gone back to prioritising the people he wanted to - his EXW and his children.
If you look back, is there any early warning signs of their unhealthy attachment styles. Because what you are describing re the adult children isn’t healthy. There seems to be some sort of co-dependency/ controlling(?) possible element to their relationships. And the children won’t be doing that alone and it won’t have been started now. Your H will have been a key part of that and it will have started when the children were younger.
There is another thread that some of us are posting on (recovering from dysfunction) and tbh it seems that the situations where these sorts of issues are encountered are when there are unresolved issues within the first family - whether that’s abuse/ toxic behaviours/ unhealthy attachment styles.
I think where people don’t have these and partners who are resolved to make compromises and make things work (healthily), these marriages/ relationships stand a much higher chance of success.
I’m sorry this has happened.
I don’t think he is done however. What you’ve had is his initial reaction/ jab at you. He will be back saying he made a mistake etc etc. Which is why, if you can, I think you need to think about what it is you want. He won’t just walk away I don’t think.