How can some one hold your heart but they cant hold theirs (im just venting my feelings)?

well im in love with my best friend. i have been for a wile now and i know she doesnt like me. we did date in the past but things ended and now were best friends. well today we hung out and she started to talk to me about this guy she likes. i didnt say anything but im sure my face or body in some way showed how hurt i was and it seems like i cant get over her. like some times i start to think that im over her but then some thing like this happens and i realize that im not and that im still in love with her. i try to give her my support like today we talked about going to the movies with a whole bunch of friends and all of our other friends would have dates so i said she can bring the guy she likes if she likes. she sounded surprised but all i want for her is to be happy. yes i rather her be happy with me but i know thats never going to happen. now there has been a couple of guys before this one but this one she came out to me and told him instead of me asking her. i just wanna know what went wrong with me. i prob treated her the best out of any guy she has been with. like i would make and buy her things and i would pay for any date that we went on. i flirted with her and idk it just really bugs me that i dont know what i did wrong. i want to ask her but i know she wont tell me the real reason. it also bugs me that i cant get over her. like i have been in love with her sense oct. thats 9 months almost a year and i still am not over her. so if you read this all just comment and say what ever you like because really i just wanna hear what you guys think. thanks guys and girls for reading