Every dark cloud has a silver lining. I read your story and I do not mean to offend you in any way, but you were way too dependent on this girl for your daily happiness and security. She isn't stable. I have some guesses on why that may be, but keep in mind they are just guesses.
From what I gather the two of you were very very young when you started this relationship. You seem to be a-ok with not having "been around the block". Your gf on the other hand wants and craves experiences above and beyond what you can give her. She's had you and she's experienced you. Period. She wants to get out and live her life and then settle down. No matter how hurtful that may be its perfectly normal.
Anytime someone EVER says that they love you but aren't "in love" with you it's over. It was over years ago. Things don't recover from that point no matter how much it may seem like they do. This girl deleted things from your computer, was rude, etc because she has a lot of built up resentment toward you. Granted, its her fault for staying, but she still blames you for making her feel guilty. The guy she "likes" is probably her ex. But if I'm right (and I bet I am) after the initial rush wears off she'll walk away from him too in search of greener pastures. It's a pattern that seems to be alarmingly recurring in people who start long-term relationships at a very young age and then abandon them after years and years. They test the water throughout and then finally leave to go chase the rush for a while. I have known a LOT of people who did this.
But....you're free. What you are "in love" with was what your girlfriend provided to you. She was a companion but she was never a true partner. The two of you have had ups and downs and rocky patches for so long aren't you ready to see what a smooth ride should really feel like?
Basically everyone in the world can tell you to stop loving her and it isn't going to make a bit of difference. You can grieve a breakup just like a death (thank you Psych 101) and that is what you have got to do. You have got to let the relationship go and start the grieving process, no matter how hard that may be. Start dating again--even if you don't feel it in your heart. Go out with friends, immerse yourself in school, work, or a new hobby. Don't go around bad-mouthing your ex or watching her house, If she has a Myspace page don't visit it, delete her numbers from your phone and pretend she was a good, albeit bittersweet dream.
And if you see her in public, don't wave. Don't let her call you and cry. Just hang up. These are the things that will show her she screwed up. Right now she is still believing that she could have you back if she wanted. You're better than that. Everyone deserves to have someone who is actually "in love" with them and you are no exception.