I often feel that I doubt I would even take her back if she tried. I could never restore the trust and she would never do what would be required.
One of the most freeing things I've ever done was to decide that an ex-gf that kept coming into and out of my life at her whim, was finished. For years she tried to come back into my life, but I had moved on, and stuck to it. I feel so free even today thinking about how if situations changed and she tried to come back I would firmly say "No thank you." I think the best decision you could make for your self is to drop the doubt, and say without a doubt, it is over and I am moving on. File for D and move on with your life. You've been stuck for so long I don't think you realize how amazing freeing yourself would be.
Also, you mention her lack of self-esteem meaning anyone that gives her attention gets her eye. What does it say about your self-esteem that you still entertain the thought of taking someone like that back? Just a thought.
Better days are ahead, my friend! I guarantee it.