[Year's_End]

Two reasons for breaking up a relationship:

1) it's simply not working (incompatible, fighting, boring, whatever)
2) falling for someone else

Since you never explained anything being particularly wrong, she probably had her eyes on this new guy while you two were going out.

Here's the thing: big fucking deal. You're 20. You've got so much time. You'll find someone else. Yeah, you know the answers, but it's the truth. It's typical to feel hurt and withdrawal after a relationship because there's an intense high you get being around a significant other. It's like having a withdrawal from a drug. You'll get over it in time...even if it takes a few months. Just get her the hell out of your life. Don't invite her to whatever it is you were talking about.