What should I do? I am having some girl troubles :(?

So, when my girlfriend first met me she was ALWAYS wanting to play the game and have 'affairs' on me, I didn't really care that much, we were young and it is not like it is really harming anybody by doing it right? I think eventually that kinda spilled into just an all around open relationship, my gf didn't OVERLY, like this to begin with cuz she thought it kinda took the fun out of having an 'affair' in the first place. Still, we continued down that path and she began to develop a bit of a player attitude in me...So then she leaves me for two years, doesn't tell me where she is going or any of that stuff, just ran away. When I FINALLY see her again, she is devastated and I can tell that she has had AS big of heart-ache from all of it. She was 12 when all that stuff from before happened, I just don't think she could handle a relationship moving SOO fast. So everything is good right? Well we are in different grades now and she still refuses to go out on a date with me, so we lose contact and, in a sense, I feel I kinda came over and spent my last year of highschool at a school I didn't where I didn't know ANYONE for NO reason at all!! In a weird way we begin to reconnect though as we still kinda are, there is a spark and when we pass each other in the hallway we cannot help but to start smiling :) SOO happy to be around each other :). So now she begins to show me what she wants out of a relationship, she flirts around with other guys when I am around, at first I feel kinda uncomfortable with it, I am all prude and stuff and want it to be a relationship between just me and her, then I start getting used to it, and I start flirting around actively as well, I even join multiple dating sites so that I can flirt around even when I am not out and about :). Now, she is becoming all prude on me and stuff and giving me the impression that she doesn't LIKE me flirting around with other people, the problem, I am just starting to get pumped over the idea of an open relationship. What is she thinking??? Like why do you think that she would all of a sudden just change her mind like that??? I am not sure whether I should continue on with the open-relationship concept or whether I should try to narrow my vision. Plus, if she really does want it just to be traditional now, it is kinda difficult cuz I lost my member id for the main site I go on, so I can't just cancel my membership. She STILL is not making an effort to get in touch and have a serious chat about this stuff, she just gives me a vague idea of what is going on her mind :( PLEASE help!!! Why do girls always seem to back-track on things that they say like that???