Okay, before people start telling you everything that you want to hear, I'm gonna stop the madness and tell you what you <i>need</i> to hear, before you go getting yourself hurt again.
The reality is this, Memalvada: she broke up with you once, and she will break up with you again. Do the right thing and put a stop to it now before it's too late to do it without having a nervous breakdown.
The funny thing about serious relationships is, you don't really learn how to handle them until you've either blown one or had one blown for you. Look at this as a new begining for you, a chance to start over with someone new.
After things are broken off, spend some time single. Let's say a few months. Reflect on the relationship. Consider everything she did wrong first, and then consider everything you did wrong (I say it in this order because you'll be beating yourself up enough as it is).
When you've got your head together again, get out there and start meeting women. Find one you like, get her phone number, wait one more day than you feel comfortable waiting, and then call her up and ask her out on a date. Have a time and place ready. Then hang up. No phone conversations. Save it for dinner.
When you're out with her, keep the conversation about <i>her</i>. If she asks you a question about yourself, answer it quick and then fire it right back at her. If it's a serious question (anything to do with past relationships, for instance), dance around it and ask her something else. Have some funny lines ready. Make her laugh, show her a good time, compliment her once and only once, do not allow her to get the check no matter how much she insists, and always get doors for her.
And above all, kiss her goodnight. This is the single most important thing you must do, because it will tell you everything you need to know about how interested she is in you. If she turns a cheek, she's not interested. Move on. If she kisses you back reluctantly, you haven't proven yourself yet, but you still have a chance. If she kisses you back and means it, you're all set for the time being, but nothing is clinched yet. In either of these two latter cases, again wait one more day than you feel comfortable, and then call her up and ask her out again.
As for how long to wait to call exactly: five days to a week. DO NOT call before five days. Why? Because that whole time that she doesn't hear from you, if she's interested in you, you'll be on her mind, and her interest in you will continue to climb as she wonders when you're going to call.
I've adapted these insights from those of Doc Love at Askmen.com. Go <a href="http://www.askmen.com/dating/doclove/index.html">here</a> and read everything he's got. It's invaluable advice that's turned my romantic life completely around.
But first and foremost, you have to break things off with your girl. For that, I have nothing to say other than to just do it. It doesn't matter how, because chances are, it'll be the last conversation you ever have.
Good luck, big guy.