You know, I am younger than you are but almost the same thing happened to me. I met this girl one day at school and I thought she was so pretty... At first the thought of being gay was frightening, so I tried to forget... But over the years it got stronger, and we both just realized that we both love each other, and now we are together.
Sometimes, you don't need to try and figure out if the person you love is also gay/bi. You just need to put yourself out on a limb. Because if you want to spend the rest of your life with that person, they have to love and accept you as much as you love/accept them. If they don't, then (sorry to say) it's not worth your love. And if she was being defensive, and she loves you back, then that's when you know you've got it made.
Basically what happened to me is that my friend and I were play fighting like we always did. It got a little further than ever before and I just said out loud "i don't want to change everything on you but I have to ask... Are we gay?"
she laughed quietly, and said she didn't know... But then we realized by then that the answer was really yes.
Your feelings have worth; don't let them fall to waste.