Look at it this way: you're experiencing heartbreak for the first time while you're still relatively young. It's going to hurt, it's going to feel like the walls are closing in around you, it's going to feel hopeless for a time. But it's not the end of your life; in fact, it's only just the beginning.

Go through all of the feelings. Let yourself be mad, and angry, and sad. Shout, kick and scream if that's your style. Just don't be self-destructive. Recognize that this, too, will pass, and you will eventually come out of it as stronger person, even though it really doesn't seem like it right now.

Man, I've had my share of heartache. I'm actually going through a breakup myself. This isn't the end, she wasn't the one, she'll fade into memories soon enough, and you'll find happiness without her.

Best advice, my friend: accept that it's over now. Nothing you can do will undo what's been done, and pushing it will only mean further pain for not only you, but her as well. You're going to go your own separate ways now. She will live her life, and you will yours. Be good to yourself, bro.