Absolutely. I stayed, and I think I regretted it - it was a horrible way to live and ended in disaster when they were teenagers.
Like you, with two small children leaving seemed impossible. I had no faith in my ability to earn or give them a decent lifestyle, was horrified at the through of them ever going to him alone for even a weekend, and couldn’t bear the thought of how nasty and manipulative and angry he would be if I did break up the marriage. So I do understand how you feel.
Would it have been better to leave? Well, I suspect it would have.
It turned out I am perfectly capable of earning good money; I would probably have met someone fairly soon too which would have helped on that front.
Even though he’s a rubbish dad he’s still their dad, I couldn’t protect them from that forever, and me being around all the time wouldn’t stop them from seeing he was a rubbish parent. Splitting when the children were young and less able to understand exactly what was going on would have been better than doing it when they were teens.
Would the split have been horrible? Undoubtedly, because we did split and it was horrible - but when it was done things were so so so much better. Which is why I say divorce is like childbirth - messy and expensive and painful, but doesn’t last forever and when it’s over it’s so well worth it.
I haven’t read the full thread but I have worn your shoes but taken the ‘stay together’ path. It did have some advantages - we had a very comfortable lifestyle and financial stability (he is a good earner). And I was able to live out the destiny I inherited from my unhappily married martyr mother - I didn't expect to be happy in marriage.
I hope you find a path you are comfortable with. Solo counselling helped me enormously.