Sometime we mistake anxiety for butterflies and sometimes we can't let go because we can't get over being rejected. You have to sit down and ask yourself (even if you write it on paper) what the good things about being with him are, and what the bad things are. The positives and the negatives. It doesn't matte how many of each there are, only that you are able to look at them realistically.
The problem here is that he's moved on....more than once. If e never sees you moving on with your life, he will always assume that you are there at his beck and call, whenever he decides to get back with you for a while and when he's bored or doesn't want to be bothered, he moves on again.
You deserve better than that. You deserve to find someone who will love you like you need to be loved. Who will support your feelings, who will be honest with you and faithful to you. It may seem at times that this is impossible or hard to find, but I assure you it's not. Just because he won't be upfront with you, doesn't mean that another man won't be.
You have to work on your self esteem. Realize that you not only don't need this man, you don't need any man, to make you into the woman you are and the woman you can be. Never allow someone to have that much control over you, that you put your life on hold. He's already told you that he's not interested in more, and I understand that since it's always been of and on, off and on, that it's hard to truly believe him, but the best thing is for you to pick up your pride and move on. There's no telling how he will react to this, there's not telling that you may not actually get back together sometime down the line, but since he has said that he just wants to be friends, then I would believe him and move on with your life.
I welcome your thoughts, let me know if you want to talk more