Well... for me, one of the turnabouts was when I had signed up for (and paid for) evening classes to further my career... and realized that there was no way in hell I could leave the children alone with AXH for two nights a week. They would simply not be safe with him. I had to call the admissions office and cry and explain and beg for my money back. It was humiliating. And all I wanted was to do something for myself -- that would benefit the family. That was one of the last nails in the coffin.
I think I started putting myself first before I left him. Or at least started realizing that I needed to. Honestly, I still struggle with it -- mostly because when I left, I was also left with the entire responsibility for the children's mental and emotional health. It was hard, and I felt responsible for having chosen an A for a father for them, and for then breaking up the family.
I realized after a while that me giving up everything and sacrificing every moment of my waking time for them was no healthier than doing it for their father. I realized they needed to see me make myself a priority, or they would carry with them the disease of codependency into their adult relationships. I guess it was a codependent thing to do, to try to save them from codependency by showing them it's important to prioritize yourself?
I also found it hard because I had spent so much time prioritizing everything BUT myself that I honestly didn't know what to do. When the kids were at his house for the weekend, I didn't know what to do with myself. I had to rediscover what I liked, what I didn't like; I had to try out the stuff I used to like to see if I still did. It was a process, but I more and more approached it as an adventure -- like "There's SO much stuff out there I could be doing -- I could just try EVERYTHING!!!"
You will find your way. You're doing the hardest part right now.