Social_Liar: I don't think anything in life hurts quite as much as your first big breakup. I know you're hurting now. However, he has decided to move on.
We grieve the loss of relationships just like we grieve the death of a person, sometimes even harder. Right now, you are in the denial phase of loss, you're trying to convince yourself it really isn't over. My best advice is to be patient with yourself. Give yourself time to grieve and to be sad. Pull your friends in close to you during this time. Stay as busy as possible, but don't be afraid to just take time to be sad.
Above all, don't jump into a rebound relationship to make yourself feel better. Grief is something you can't go around, you have to go through it. I know it hurts now, but you won't feel this way forever. When you've been "dumped" by the person you love, you feel like you're unlovable and that you'll never be happy with anyone again. Those are lies that our low self-confidence tell us. You will feel better, and you will love again. Don't hesitate to come here for support. You may give in to the impulse to contact him at times. That's normal. Just don't be surprised if he doesn't continue to feel the same way he does not.
Hating him will accomplish absolutely nothing and can actually slow your own healing. The best way to get back at him is by taking care of yourself, bringing the things in your life you want, and by moving on. Hating someone just drags us down and they don't care.