Dude, first thing, GUY HUG!
I know exactly how you feel and it's pretty ****. You need to pick yourself up before it's too late.
I shut myself away from everyone for months, didn't go to Uni, barely talked to any one or ate, it really got to me. These are emotions and feelings I felt then, that I never wish to feel again. It's drastically effected my education (i'm only just going to scrape through this year) and my social life. I feel stupid for letting myself get that low, however I'm back on track and could never feel better! ^_^ You need to feel like that before going down the depressive road. Cry, get it out of you and then try to forget. I know it's hard, but it's the only way.
I'm guessing that it's not the fact she's split with you, but again, similar to my own situation, the WAY she split up with you. I can't guess why she did this to you. You need to take it on the chin though and realize if she was prepared to hurt you in this way, by sending someone else to do her dirty work, then she's not worth it. You, YOU, are better than she is.
I still don't know why my ex split with me, now I don't care. Don't be embarrassed or feel silly about it, she's hurt you in a way no one else could. She is not worth it though.
Get it off your chest and move on. Please. You're young and there's an entire life ahead of you! Enjoy life and take this experience and remember it. Remember the good times that you had with her, and cherish them, but don't dwell on them (contradictory I know).
Love is wonderful thing, it really is. This will not burn you out this early though. I'm telling you :P
Good luck ! If you ever want someone to talk to just drop me a PM.
Hug!
