How do I get over this rebound.?

She was always one of my best friends. She was dating this kid for a year and broke up with him but before they even broke up we were already "talking". This was like 5 months ago. When she broke up with him she told me she would kill to have someone like me.So I steeped my game up we talked every single day. Everything was looking great, all of our friends loved us together. shed come visit me at school. I told her how much she made me smile and I was so happy around her she told me the same thing. She even told me that she wasnt going to use me as a rebound (I believed it). All she said was she wasnt ready for a full committed relationship and we should take it slow and we did. We hung out every single day all the smile and laughs we could talk about ANNYTHING and have fun with it. We went and drank and partied together. Kissed and made out and did all those kinds of things. Everything but sex. But we were very close to doing that. But one day Like a month ago she told me she was going to this place with this other guy. And then the next day with him again and then she randomly just started dating him within that week. I sit here and wonder what all fell apart? I didnt do anything wrong. She just randomly said things changed. One week shes sleeping in my bed and a week later shes dating another kid. Im befuddled. For the last couple weeks shes been texting me about how it should of been me and how much she loves me. and she doesnt want to be with this other guy. I was still totally confused. Emotionally wrecked. Everything just randomly fell apart. She just deleted me on facebook I didnt do anything wrong.I Treated her amaizng. She was the girl of my dreams Ive wanted her for years! My one friend told me she probably me as a rebound. Did she use me as a rebound? Anythin, Any advise helps. I really love this girl. And I want her back. :(