What you need to understand is why you want this man when he is through with you and wanted nothing to do with him when he adored you and looked at you like the only woman in the world. The problem here is that you want a man that you can't have and don't want a man that you can have. You need to find out why.
Your clue lies in your first family. Read my Advice Archives under repetition compulsion and unfinished business to understand what wound from your past is causing your problem. If I had to guess, I would say that you are no stranger to disappointment. You probably loved a parent who wouldn't love you back. This experience would lead you to push away love when it's offered (because it's too unfamiliar and scary for you) and/or cause you to choose someone who won't love you back. Either way you are left yearning, which is how you felt as a kid.
This recreation serves two purposes: first, it keeps you locked in the comfort of the familiar; and it allows you to struggle for a happy ending (see my archives) in which you finally win the love of the parent who won't love you. The fact that you can't stop thinking of your ex., tells me that you are still dreaming of achieving your happy ending. If only you could get back with the guy who wants nothing to do with you, you would feel that you succeeded in winning the love of the parent who didn't want you.
I am afraid that there is no happy ending for you in this scenario. This guy has been pushed too far away to ever come back to you, from the sound of it. Start therapy now, and talk about who wasn't there for you as a child, grieve, rage, and free yourself. When you heal yourself, you won't feel driven to push your next boyfriend away and turn him into your uncaring parent. Understand that this pattern you are locked in (pushing the guy away, then yearning for him when he's distant) has been your way of trying to heal the childhood wound that still festers inside you.
When you heal this wound, you will be free. Then and only then will you be able to create a healthy relationship in which you will allow love to enter your heart.