I was in the same exact place as you nearly a year ago...and it feels a lot shorter than that. And I am fine, living a great life and actually having more fun than I ever had with my ex. You can look up my past threads too (I also wrote some under the name Lals49). You might be able to identify with a lot of my feelings, and i got some amazing advice that may help you, too. I didnt believe it when people told me that Id get over it. I didnt believe it AT ALL!!...I thought it was a lot of nice, inspirational babble that people say when one goes through a tough time. But the amazing thing is, you really do. The worst part is the first bit...b/c you go through withdrawal, a lot of emotions, and a lot of pain. But eventually, you start realizing that you dont have as much pain, and, little by little, you lose the pain completely and instead you gain greater trust and confidence in yourself b/c you realize that you are fine without him...and a stronger, more intelligent person at that!
What I do know for sure right now is how you are feeling, and it pains me to remember how that is. I would really suggest not talking to him, but I couldnt help it and I really tried to get answers from my ex...which got ugly, b/c he broke up with me out of nowhere, but then dragged the breakup out for a long time until I found out he had another girlfriend (Im not in any way saying that is your ex's situation). But in reality, even answers dont help. Its really hard when someone breaks up with you on a whim, but no matter how much you want to know why, you probably will never know. I tortured myself for quite a long time wondering 'why?'. Im at the point where I do things for ME now. Everything i did before ALWAYS had him in mind...and thats just not right. Ive accomplished and seen more in this past year than I ever saw with him/would have seen had I stayed with him. I know right now that all of this is hard to believe, but I can guarantee that, over time, you will get to the point where you look back and smile in relief. Because you will realize that no guy that is the one for you will ever be able to walk away from you just on a whim.
Make sure to keep yourself busy and put all of your energy into your friends...times like these make you realize how important they really are. Also, I got a lot of counseling for awhile which helped me stop obsessing and helped with the depression I was in...so you might want to look into that too just to have a support system if needed. And keep posting if you need to, these boards really do help.