WhiteWax, I know it's hard, but I agree with the other women who've posted to you - your ex is not able to be a partner, friend, or anything else useful to you right now. Is it possible that could change in the future, yes. But that's not important right now. Right now you need to find the support structure that you need to get through your current life situation.
My experience of this pales in comparison to yours, but after living with someone I loved for two years, he decided to attend grad school about 10 hours away. I started making plans for a job search in that area. He moved first, and within a month, he started saying things about not being sure that our relationship was worth the move for me, etc. I was heartbroken - he'd been my best friend for so long that I couldn't imagine losing that. So we kept in touch and stayed "friends" for the most demeaning, unhealthy five months of my life. He wasn't trying to be cruel, but the effect was devestating. I couldn't even begin to move past our romantic relationship under those circumstances. I didn't begin to heal until I told him I couldn't be his friend just then, no matter how much I wanted to, and that I'd get in touch when I could be a friend to him again. Then I stopped taking his phone calls, which is one of the hardest things I've ever done.
I know you can't cut him out of your life - he's the father of your children. But try to get as much distance as you can for the time being. You need to have contact with him, but you don't have to be his friend right now. And definitely surround yourself with people and influences that give you hope and strength. Focus on making your life and your children's lives what you want them to be regardless of his role in them. He clearly can't give you what you want from him, so you need to focus on finding other ways to make yourself happy.
If it gives you any hope at all, six months after my breakup with the above mentioned partner, just when I had begun to accept that I could be happy even if he didn't come back to me, I was offered a dream job in another state and met my incredible husband. That breakup left me open to options that I could never have considered while in the relationship. I'm not an "everything happens for a reason" kind of gal, but often the silver lining of a painful change is that it creates new possibilities, some of which can be quite wonderful.
Sorry for the book. I've just been thinking of you a lot and hoping that good things come your way.