Do you think I've fallen pretty hard for one of my best friends?
Tell me more about it. What feeling do you have about it?
I feel head over heels with her. A kind of feeling I never felt before in my life.
That is an interesting development.  It is okay to have feelings for a close friend.
You see, I was feeling down a bit after my past relationship ended, but she was there for me and my heart is starting to twirl.
It sounds like you are indeed falling for her, so maybe you should take her on a friendly date and tell her about your feelings. At the very least, you made an attempt, and who knows what will happen in the future.