@Mothersdayschmothersday I can feel your anger in your posts and I'm going to be very blunt (my asd talking sadly so please don't think I mean this harshly)
I think your anger is at the wrong person. And I wonder if the children are picking up on it.
Sm says your children are a guest in their home, so was this a response to the children maybe treating the house poorly be being messy and asked to tidy up a spill ext/ playing up ? You know kids, your their mum they will want to please you. They can probably sense your contempt for sm and want to say the right thing. They could be stuck in a loyality bind.
So my exDH was kicked out by me 8 months pregnant with my Dd, after finding out he was having a long standing affair after the loss of my first child. He said grief made him cheat but that's a story for another day. For a very long time I was incredibly angry at her until a friend pointed out to me that it was my ex who broke his vows and my trust and maybe I was angry at her because I couldn't sort out my ex being a twat so I was angry at the person who I thought I would have more success at changing. Does that make any sense ?
And my Dd was picking up on it and acting up. I could say it was just deserts (my ex did marry the ow so now Dd sm) but it was causing my child pain. And although I was still really cross, I toned it back massively. My daughter was more settled and years after i still think my ex is a twat 😂 but sm cares for my Dd because they were able to build a relationship outside of a loyalty bind (one I didn't even realise I had created). Although it stung at the time. I know see more people to care about my Dd the better.
The problem with being angry and hurt is the people who become part of the collateral damage that weren't supposed to be - my Dd and me. It was freeing and frankly I operate on a unless it's a safety issue it's just not my concern. Hard so bloody hard.
But on the reverse I am now a sm (worth and hard) and god it's hard. I love my DSC dearly but she hated me for a long time (parents split years ago, because every kid deep down wants their parents back together) I'm more like a friendly aunty or another trusted adult. It took time for the dust to truly settle. I'm sure her mum had DSC ranting about me for a while, but when mum said hey give her a chance, she did. Thankfully. And me and mum get on (usually) and DSC comes to me with things she feels she can't ask her parents ect but I know I'm not trying to replace mum in anyway and I think sm think the same.
I can see your hurt and frustrated and that's completely normal. But I do think focusing on her stops you addressing the problems with him. She may be a issue but he's a bigger one.
I also have sympathy with the abuse you faced with your ex. I work probono in the sector and from what I have seen. Your perspective gets fucked for a long while post being with someone like this because your so used to him blaming, you,the kids, the dining room table rather him. It's engrained but you can and will unlearn it. But I promise you if you wanna tackle this. Change the focus. Otherwise you give him the tools to blame someone else for his actions and that helps no one.
There's a lot of grey in blended families, and for everyone's sanity it's best to just avoid trying to influence another house. The kids will see it eventually as long as dad doesn't convince them that everyone else is to blame for his failings.
Happy to chat in pm if you need to x