Hey Monkey, welcome to the forums.
Just like to tell you that I know what your going through.
Im a year older than you, but still in your situation.
Unfortunatly, the fact that I am in this situation means that I dont have much advice for you.
Only thing I can think of is starting to make moves on the new girl before she becomes too much of a friend. I only fall for someone when I know them properly and am realy close too them, but by then I am too close and just become a best friend. So Im stuck. But you seam to have the hots for her already, so make your move! (after reading everyone elces advice 1st, lol)