I think people universally expect life to become better once they've made some steps in the right direction. When life doesn't immediately respond that way--when we still have problems and feel like crap, we immediately conclude that whatever steps we have taken haven't worked, will not work, and we are doomed, so we might as well keep doing what we've been doing.
ALL change--even the most healthy and positive change (and sometimes ESPECIALLY that kind of change) is painful, difficult, and takes time. The rewards are down the road, but it's hard to believe that when we are sitting there, having done/doing the "right thing" and everything feels sucky.
What your life has been like has, no doubt, made you a little bit "insane." I know I've been "insane" at various points in my life. This kind of "insanity," however, isn't permanent, and sometimes doesn't even require professional help (though such help is sometimes, well, helpful). It DOES require effort and patience and willingness to tolerate a degree of uncertainty. Going on into the future on your own, without him and without the future you envisioned for yourself, is scary. At least with him, you knew what to expect.
But you can't grab a new future for yourself while you are desperately holding onto the old one. He has displayed zero interest in changing, and he wants you gone because you want him to change. He's MADE his choice. If you can't make your own choice, you are still stuck with his. Even if you wear him down and he takes you back, it won't be with any intention of changing his own behavior. You'll just have a repeat of the past however-many years. Meantime you will be getting older, sadder, and feeling progressively worse about yourself.
Letting go, and moving forward, is hard at first, but eventually momentum kicks in. Think of a bowling ball and what it takes for it to change direction and start moving the opposite way--basic physics. It has to stop, and then there has to be a significant amount of force applied before it starts moving, but once it does, it ROLLS.
Lots of us here have successfully changed the direction of our lives. It is difficult at first but becomes progressively easier with time and effort. If we could do it, so can you.