Hahaha....that is so funny! 
Hmm...take it from ron33, he is correct. Trying out that kind of
stunt on your graduation day in your gradation gown might not seems
to be that romantic after all. What is so romantic about it anyway?
The gown? Or the mortar cap?
She is probably treating you as her close friend. Probably someone
she trusts with all her problems. So this kind of girl is very
difficult to be your gf lor. Firstly, you know too much of her
s.h.i.t already. Secondly, you are not new to her...so, not
exciting enough for her to be with you. She probably felt that it
will be boring for her to be in a relationship with you. Thirdly,
you probably do not have the qualities that she wants and is
looking for in a guy to be her potential bf...if not, she would
have chosen you ages ago.
I hope that you don't feel sad over it, but instead be encouraged
to take up the challenge and turn the impossible into possible from
this moment on.
You should know how to go after her appropriately since you know
her so well already. Besides you got a gf before, so you should
know girl's thinking a bit.
Do your best to go after her if you really love her that much.
Otherwise, read my signature. 