Rent the movie "She Just Not That Into You".
IMO - She's just not that into you.
The harder you try, the more your freindship will suffer.
You need to back off and just become a freind, all the while hopping she will suddenly see what she has right in front of her. Endure the other boy freinds she will have and learn to bury your love deep in a place that will require mega amounts of therapy later in life.
OR
Just pose the question to her, and if she says no - MOVE ON.