I'm in love with my best friend, what to do?

I am in my early twenties and I am head over heels in love with my best friend. I have known her since grade 7 and I am already five years out of high school. So that would be almost 11 years. We talk almost daily. I have tried to forget about her by dating other girls but that just doesnt work. I have still loved her through out her boyfriend(s) of 2 years. I told her I liked her back in high school, but she didn't feel the same for me and it was very weird and awkward between us for quite some time. I mean she is still my best friend no matter what, but I think i'll always love her. Lately she has been more flirtatious towards me and gives me signals, but she literally just got out of a relationship and had four other guys from work confess their love to her. Should I just deal with my heartache and hold it in like I have for 11 years or should I tell her? I want this girl in my life even though it might just be as friends but sometimes it is just too hard emotionally.