I am sooooo lost?

There is this young lady, who is my best friend. We have known each other for 2.5 years. We are really close, and share each others secrets. The problem is I have fallen for her. I have tried at least 5 times to make this relationship more than just friends, but she does not like me in that way. During these 2.5 years, she has gone out with "losers". She keeps getting her heart hurt by these dum-dums. She talks to me about them and about the idiotic things they do to hurt her. Sometimes I just want to say, "Stop dating these idiots and be my girlfriend!" What should I do?