This is another typical sad ending story which is the reason why ladder theory was made.

Don't fall prey to that 'nice guy' attitude. Don't be that wimp with no backbone who is doormat enough to listen to a girl's emotional problems. Once she sees you as a friend and not a man, there is no way back. Unless you are capable of changing the way you interact with her completely. I doubt that you can do that if you have been her best friend for a while. Just move on and look for other girls. If you can't do that, then well, tough luck bud. Everyone goes through some kind of phase like that.

If you can't believe me, you gotta read this.

Dating Secret Exposed: Why Nice Guys Finish Last -- Yahoo! Personals