I have feelings for my friend

Hey guys, I’m a senior in high school and I identify as straight because I’ve only ever been interested in guys but like two months ago a developed a crush on my close friend, that’s a girl, out of absolutely I where. She gets mistaken for a lesbian quite often and gets kinda upset about it. I have a feeling she’s not completely straight though. She has feelings for another guy right now also I’ve never liked a girl before. I have no clue what to do, have any advice?