Well, to be honest, it really wasn't a good idea to "dump" him in the first place.
You may think I'm being harsh, but you did get yourself into this mess, and there is a chance that there won't be a way to fix it. I know if I had a boyfriend and he "dumped" me, I would have a hard time taking him back - even if he told me he didn't mean it.
So I guess talk to him, no one wants to be living a life of "what-ifs" - what if I talked to him and he DID take you back, etc. It's important not to brush it off though - tell him YOU were wrong, and that you were insecure and concerned about a long distance relationship (well, I don't know how far away he's moving, but you get the idea), etc.
Even if things don't work out, remember how young you are, and how much time you have ahead of you to date - and now you'll know not to make the same mistake twice.
Good luck, hope it works out ;]