I don't feel much like reading the rest of the responses you've gotten, so I'll through this at you: Ow. It hurts. Being double-crossed is a bitch, but it learns you a lesson~
You're young, with so many years ahead. Don't spend them mourning over some dimwitted nutjob who wants nothing to do with you.
Getting involved with someone is great! Especially if you come to care for them! You seem to have waited long enough, with those 3 years mentioned. If I were you, I would cherish the lovely memories of the years, but move on. Try not to think of your ex much, and they'll eventually fade.