My Girlfriend or is she?

My Girlfriend Name Is Emily http://tinypic.com/view.php?pic=qnv80m&s=7 ( Pictured) who is a Teenager who's 16..... and i have been With her a Long time........... Since i been with her she always hasn't really treated me as a boyfriend.... she gives me this funny look where she has a scrunched up face when she's mad but she gives a curious look of it too.... everytime i am with her she does it and when she don't she seems Unbothered. i felt she never treated me the same as everyone else always thought i was boring or not good enough for her to meet certain requirements.. i always would buy her anything and acknowledge her but the more so the more it seems she takes advantage of me. couple of weeks ago she confessed that she thought i was a loser who doesn't even answer her when she speaks..... that is untrue... she never has given me her phone number and i am always chasing after her like a lapdog. i feel rejected, i wouldn't class myself as a stalker more of unrequited love. i was totally in love with her .... anyway she also said couple of weeks ago she preferred guys with blonde hair and pale skin..... she always trys to hide the fact she's Bisexual.. anyway one of my friends who know her told me she is cheating on me with a 54 yr old man and i know they wouldn't say this if it wasn't true there said either 54 64 or 74 but i am guessing 54. weird thing is my stepdad is 54 and it gets me thinking you know.... i can't ask him as he won't admit and it is ultra hard to to get evidence. i don't even know myself yet all i know is positive she is with a 54 yr old man.she told me once age doesn't matter but i didn't know she ment like this i thought she mean't distance between age between young people like say 21 and 16 for instance not 54 and 16. i have always told her please tell me if you have cheated or if you want rid of me but instead she lets me on.... she always avoids me too and i always tell her that and she is like SO. i feel as if i died she would just say he is dead would be a little shocked uncaring and that's it.. what do i do ??