I can tell you, your children will eventually see your side and they will eventually see that your stbx is the awful, controlling, abusive man he is.
My Mum left my Dad when I was 7. I was devastated and hurt. I loved my Daddy so so much and I cried for him every single night I went to bed.
Once I got into my teens I saw how much he didn't really care and I was able to see things from a different perspective.
My father was an abusive bastard. I remember him physically throwing my mum from one end of the lounge to the other. Picking up and beating my sister who was 12. My mum did everything in the house, she worked full time, raised two girls and looked after his terminally ill mother. He was and still is a shit father.
My sister, incidentally, who was 13 at the time of their split, blamed mum and had awful arguments with her (she really hated Mum). Some years later, she, like me, saw that it was better that Mum had left.
Keep telling your children you love them and that they are ALWAYS welcome to come with you wherever you are... and in time (as painful as it will be in the interim) they will see you made the best decision for all of you.
Thinking of you OP
I think you are wonderfully brave (even if you don't feel you are)