Fantasies of my friend

Can some one please help me understand why I'm fantasizing about sex with my new female friend. I've met her three times and we really seem to get along but these feelings are impulsive. I've dated only men in my life and I've had one sexual experience with another woman and I found it boring tbh, and the only other time I've had sexual tension towards another girl was 10 years ago in high school with a girl i was becoming friends with. I'm just trying to rationalize this and after sex with that one friend the friendship ended. I don't want to lose this new friend especially since I don't currently have any.