What do I do? I don't want to let her go :( HELP?

Please help me, your help would be greatly appreciated. I know its a lot of information but please bare with me it's a very difficult thing for me to overcome.

Ok, so I have like this girl for a long time now. And we have become very close friends throughout this time that I've liked her. We text and chat on facebook all the time and I just recently about 3 weeks ago, took her to a theme park and it was amazing. But ever since then, it was'nt just a crush anymore. I knew I had loved her now, because she would be all I thought about, all I dream't about at night ect. But just 2 days ago, I had her over at my house and her bestfriend tagged along and so did my bestfriend, all at my house right. Now my bestfriends knows I fell in love with this girl, it just wasn't a secret to him anymore, he guessed because it was obvious to him. But while me her went to the store to pick up something, My friend was left at home with her bestfriend for a little bit, and out of the blue, her bestfriend asked my bestfriend if I liked the girl I like. So he was honest and said yes, he does a lot. So that was the end of the line right there, her bestfriend knows now. So now I have to tell this girl that I like so I did it like a man without any fear. But sadley she said she just doesn't have those type of feelings for me, but she also said I will always be one of her best friends and that I will never lose her. But it doesn't feel like my chances with her are over yet, so i'm going to keep being her good close friend but I dont know how I could ever get a second chance with her? Any thoughts about what I should do?