What should i do if the girl i love doesnt like me and wants to be just friends.?

Ok sorry this may be a little long but i love this girl who will remain nameless and when i say i love her i mean i have loved her for 4 years straight now as we have been what she thought was best friends for a good portion of it and i pretended that i wanted to be best friends too because i didnt know how to express my real feelings for her. Well i should start from the beginning at the beginning of when i met her i really liked her and she liked me too but i didnt know that and i found out the summer after that schoolyear and i asked her about it and she said yes and i told her that i liked her too at that time and that led into us talking and having a relationship but we werent going out and then she went away for a week and came back a different person and didnt want to have anything with me anymore. After that i didnt really want to talk to her anymore and for a good amount of that school year i ended up making her jealous of another girl i was with in the time i was mad at her but it didnt lead to anything we became friends only because she wanted to and i thought it may lead to something else between me and her but it didnt and she told me about her boy that she liked and i just remember wishing it was me but keeping it inside and pretending like it didnt bother me. The next schoolyear we were still friends and i met another girl but she wasnt like the girl i loved but i stayed with her anyway because the girl i love didnt want to be with me anyway and eventually the girl i was dating told me i had to stop being friends with the girl this whole thing is about and i didnt object because as far as i was concerned nothing would happen and i didnt want to be friends anyway i wanted something more so me and the girl broke up after 10 months and after a few weeks after me and the girl broke up i called the girl i loved on the phone and asked if we could be friends again and she said no because i gave her up for the other girl and then this last school year she was in my 3rd period class and when she saw me she decided she wanted to be friends because of how much i didnt care( she was wrong about me not caring) but we became "bestfriends again and we hung out alot this year flirted alot but it didnt lead to anything until i asked her to junior prom and we went together and danced all night i wanted to make a move and kiss her for the first time and i was going to do it at the last slow dance there was no last slow dance unfortunatly and nothing happend once again we took a walk at her house with some people after prom and instead of doing something with her i decided to smoke instead this was the last time i ever smoked and ever will it was the biggest mistake i made ever i think something could have happened but i prevented it then a few weeks later i told her how i really felt and told her how i liked her for so long and she was shocked and told me she wanted to be best friends and i was crushed so i was sitting outback of my house on a lake watching the sunset and i decided to turn to yahoo answers for help so please let me know what you think i should do any help is appreciated thanks all!