I’m really sorry you’re in this situation, where you don’t feel as if you’re the master of your own fate and are waiting on someone who doesn’t seem to know what they want. I’m not perfect, but I can say: as much as is possible, you can try to live your life following what YOU want. Not waiting for what someone else might, or might not, want from you.
So, to that end, I think it would be a wonderful thing to get your feelings out, and express them to him, in a letter might be the best way to do that considering your past experiences with him. And focus on what YOU need out of a partner. Then get it out there – and let go. It’ll be really tough, I know. I’m sure you’ve considered this already, but how safe would you feel, going back to him? I wouldn’t. I’d always be scared he might change his mind for no reason and leave me…you know?
I have no idea what your practical situation is, but I’d try to focus on me and creating a safe haven for myself. And I hope you don’t mind my saying so, but if I had faith, I would entrust the situation to God. I’d pray every day. I’d even ask a friend to pray with me. All the best