At least you were able to date the person you liked. The girl I like is currently unavaible. And the "currently" is optimism.
But as for your situation, you must have that best buddy(a male friend, usually) that will support you and help you while you're going through this. Try talking to him. And as for the girl, well, that's life. You can't just sit and cry in a corner. You gotta stand up, man up, and try to get her back(not by force, romantically, of course). But if that doesn't work, and there's no way you're getting back together... then move on.
It's not easy. You'll still think about her. You'll miss her. Maybe for days, maybe for months, maybe for over an year. But you can't let the pain stop you. Be stronger than it. I know it's hard AF though.
And at least you're still friends. Perhaps you can still talk to her and have fun with her in other ways. I know this is not as nearly the same as having her as your GF, though. But at least it didn't end the worst way possible.