I really like ths girl and need some serious help. Please try help me.?

I jst turned 16 and i like (even love) this one girl. Her name is emily. I met her at school when we were both 12 and i havent stopped liking(or loving) her since. i would even put my life on the line for her. The problem is for some reason i have acted distant with her so that i hoped she would take more interest in me. we once nearly kissed and that was when she liked me (when we were 13). Now i feel as though she would never date me. she is always acting like she likes this other guy. on odd occations (like school camps and parties) we really get close and i show her what kind of person i am. but for some reason i can never make my move from there...im in her cl (grade 10) nad we see each other nearly ervery day. but nothing ever seems to loo positive between us. in grade 8 she got cross with me and we stopped being friends i have been trying to build our friendship ever since. the problem i have is i always wnat wat i cant have and when i have it i dont want it anymore.