Dude, I went through the same thing in high-school man! Had a g/f for 3 years, found out she cheated on me, we broke up, and man was I depressed. It took me a good 2 months to actually "get over it". But in the end, it was probably for the best. As much as "I loved her", I think it was better off. After the break-up, I finally got my license, got decent job, saved money, started college, and ended up getting the car I have always wanted; my GP! Sometimes, I wish we would cross paths and I would show her everything she has missed out on, but it's not even worth it. Now I got me a new g/f, she's outside sittin' in the driveway, that B**** costs money! haha.
But seriously, I hope you can get through this tough time. Time heals! (slowly) ...and all those other cliches (sp?) I def feel for ya man! (NO HOMO)lol