My first heartbreak took me a long time to recover from since I had invested a lot of my feelings into getting to know the person for about 3-4years (talked almost everyday). It hurt a lot for a long while, but I got over it eventually by just not thinking about the person (whenever I started to, I'd stop myself), and also got rid of anything that might remind me of them xD.
My last one, I kinda did the same thing. Mostly, what helps is just not letting yourself brood over the memories/person (stop every time you start to) and distract yourself with work, anything you're passionate about. I think best way is just focusing on something else you care about, have fun, and keeping yourself busy. Hanging out with friends can help too.
Since you're 18 in college^^ you could focus on school to help get your mind off of her. And there are chances to meet new people too.
Don't torture yourself with imagining her with the new guy and don't stalk her (at least until you feel you're finally over her). >_< What I mean by stalking is -> checking her Facebook, finding out what she's doing, etc. it'll make it harder to get over. You'll need some distance to recover.