What should I do?

First, welcome to EC!
I have fallen in love with one of my straight friends before as well. The thing is that I would picture us together all the time in my head and sometimes I would keep telling myself that he was gay when he obviously wasn't. Don't put yourself in the same complicated situation that I did. If you really like her and you are really close to her, tell her that your gay first and then take baby steps from there. Don't keep falling for someone who isn't going to fall for you. You'll just get deppresed and miss out on other opportunities for love.
Whatever you do, be safe. I hope everything works well for you.