I'm sorry for your loss. Getting over a relationship is not easy especially when you thought everything was going well and the other person blindsides you. I know you are reeling right now and all the "don't worry and just move on" won't help at this point in the grieving process.
The best thing I can tell you is don't break crazy. This happened to me in college with a girl that I was ready to marry. I lost it and unfortunately broke crazy. You know what I'm talking about the whole "why, why, why" thing. I called her, talked friends ears off about it, tried to get information on who and what she was doing, etc. etc. etc.. No matter how bad you want to do these things and no matter how bad you want to understand; just stop, make it a clean break, and put yourself on lockdown. The only thing worse than getting dumped is turning into "that guy" who can't get over it.
I'll try to make you smile/laugh by telling you one of the things that happened to me. A few weeks after she ended it I called a female friend who lived in the dorms because I was feeling down and wanted to talk to someone about it. Her answering machine picked up and I left this horrible, sappy, woe is me message about how I was devastated and what did I do wrong etc. etc. .... Well, a couple of hours later the friend calls me back and the first thing she says is "I'm so sorry about what just happened."
She proceeds to explain that she does not use the school's provided private voice mail system, but a personal answering machine that she brought from home. You know the kind that uses tapes and has a speaker so that your message plays out loud for anyone and everyone to hear. Yeah... well "when you called I obviously wasn't here, but your ex was visiting my roommate and they overheard your entire message as you left it". 😱
Call it what you want, epic fail, living in loserville, or simply being a moron. The point is don't do what I did, work through your grief privately as best you can and maintain your self respect in the process.