I've said before here, my advice is usually somewhat vague and question based. I don't feel it's my place to tell people what they should do (for the most part). I try to get them to think and solve their own problems, hopefully with a little help from my experiences. And that is why I don't post a lot, I usually just try to help the people that I see a bit of myself in.
That being said, I've got you thinking and that's good. But hard. No one said mirror work is easy.
You've described your STBXW along the lines of a brick wall, ice princess, something like that. But someone in your small group said you don't know what's going on inside her head. I think you also now realize that you portray yourself to her in a very similar way.
And I think if you were completely honest with yourself, even after all that's happened, if she showed up at your doorway begging for a second chance, you'd give it to her. And I'm not trying to blow smoke up your you-know-what or give you false hope, but what if one of you opened up a crack. What's the worst that can happen? She can continue to be the ice princess so what have you lost? She could be friendlier to you and that's only good for the girls. Or she could start to see you different.
What have you got to lose?
Look, boundaries are good. But if she doesn't cross one or you can be a bit flexible ...
Listen to her. Don't argue with her. Agree with her. Just once.
See what happens.
I mean this IS a Divorce Busting site, right?
Everybody hurts. It's part of life. Don't miss the good stuff.
