Can't get her out of my head...

. I was introduced to this girl before I got to college by a good friend. They hang out 2gether while at college, so when I use to visit her there… we hung out I thought this girl was funny, gorgeous and nice. Well, we hung all together and after a lil while I decided to ask her out. She said yes and then said no….. I was pretty cut up. A few months later I ended up going to the same college as my friend and HER. Things went on and off between us for awhile, I thought she was into me and then a lil while later she didn’t seem to be. We hung out with each other once in awhile.. but then this year we had a class together and so started see each other more often. And this is when I could see she liked me, we ended up getting together at a party 1 night. From there we started to go out with each other, at the start we were having fun and were into each other. But as time went on I started to change, for the worse. I felt that she didn’t seem to make time for me at college, we only did couple things on dates, BUT the entire time I knew what I was doing was WRONG and STUPID and shouldn’t have acted the way I did. I knew I shouldn’t have done it all, but I had a hard time figuring if she was into ‘us’ as much as I was because she was closed off and kept her feelings to herself. Apart from just hanging out she never drop hints that she was into me.. so I started to 2nd guess all the stuff I was doing. This changed our relationship and we decided to call it quits because we weren’t having fun anymore. I realized this was a mistake the second she walked away from me, so I called her a few days later and asked if we could wipe the slate clean and start afresh. And I said I will just be myself this time round, but she said she couldn’t go back to the way it use to be. That hurt but I knew I had to move on, and when I finally saw her at college she seem to have moved on or wanted to make me jealous, she barley would speak to me and flirted with a friend of mine right in front of me. I really want to get over her and move on… but can’t seem to get her out of my head. I still really want her back. I wasn’t in love with her but I want can’t move past her since I have liked her for so long. I want to know what I have to do, to either get her back or force myself to move on?? Cause if I don’t… this girl could have an impact on me in the future. SOMEONE PLS HELP…..