I need some help with this girl?

We our both fifteen, here is where it starts. I was trying to get with her best friend (Sam), but her best friend wasn't in to the whole hook up thing and stuff so that was basically the end of that. So I though, then about two weeks latter I called her friend up (Sam) and she was like here, talk to Kaitlyn. So I did, we started texting a lot and calling some nights and I had a little crush on her, and I think she kind of felt something but not enough to really interest her, then it happened. She said I was her "best friend." That’s how we acted we texted all the time as I was her best friend we talked about me and girls, her and guys, one night we talked about her Romeo, and I couldn't help but want to scream out "I can be him." Lately she and her boyfriend have been fighting and there breaking up, so she and I have been flirting. It’s mostly me flirting but she contributes, and now we have moved in to a friend with benefits thing. This switch from best friend to friends with benefits has happened in a week, and I have been in Vermont the whole week. so when I get back were going to hook up, and we both keep talking about it and flirting around it, but i already want more, and I know the more we hook up, or even hang out I am going to want more then that. I don't want to freak her out and be to clingy and stuff so I’m basically asking what are the guidelines what can and can I not do, and what can I do to make her fall for me?