Don't get involved in relationships. It's not worth it. If you have never dated before, never had a girlfriend or anything like that, Don't, trust me. Going through the heartache and the weird emotions and the shit isn't worth it.
Trust me. It isn't worth it sitting there while your ex tells you she has two dates with two different people the same night you broke up. It isn't worth the stabbing feeling in your gut when she says she's interested in them, or that she had the best dream ever where she was over you.
It isn't worth being scared about her going out and being a complete whore and making out with a bunch of guys who want nothing more than to get in her pants. That means you meant nothing to her, and that hurts even after a breakup.
It hurts to see the total burning of bridges, the hurtful words just to get back at the person. It hurts. It isn't good. If you think you can hold in emotion and not express it, I challenge you to break up with someone you love. You wont be able to hold SHIT in. And there's no way to deal with it, really. It's like a cold... you just have to deal with it. You have to deal with the second thoughts, the changing of boundries, the jealousy, the heartbreak, the disconnection, the burning of the bridge, the sneakyness, the trash talk, the divided friends....
It sucks.