GIRLS PLZ HELP!! why is she acting so mean?

i told her i liked her and never made a move. after i told her, she wouldnt talk to me but she would always smile at me whenever i looked at her and this went on for a week, then she completely started ignoring me and trying to make me jealous by flirting with other guys in front of me, this went on for a month or two. Then one day she randomly gave me her blackberry pin...then i messaged her and she never replied. Then one day, she just messages me that she needed help fixing her phone (supposedly why she never replied), which i was foolish enough to do, then the next day she was makin out with this guy in front of me with no regard that i was there and she knew she was hurting me and they werent even goin out yet, then she just comes up to me all nice and crap and talks about how her phone was broken and was all nice to me, and she would call me by my nickname that she had given me and would be the only person to call me that but had taken it away during that month, then she would try to talk to me when she needed help on her test, yes i kno i was being used, by rubbing her hand all the way down my arm, then she moved to the seat in front of me and started stretching back and putting her hair in my face, then she kept trying to get answers again, but then i would ignore her and she would get mad and threatened to delete me from her blackberry messenger, and then just stayed quiet with her head down. then the next time i saw her, they we're officially going out, and then she started giving me the cold shoulder again and only talked to me when she needed me, BUT, she is in love with my phone and she is dying to get it...but when i put that im getting a new phone...she messages me 'gimme ur bold <3' and i never replied...why does she expect me to give her a $500 dollar phone for free... jsut becuase i like her?, how do i get her to stop using me, on the last day of school she just said 'wassup jorge' and said wassup, then she gave me that wassup nod and we started doing that back and forth a few times.. she never brought up the text, but could she be pissed at that...we're both 15