Best friend

Sophie
Me and my best friend are so close at the moment and a couple of months ago she broke up with her ex boyfriend. Recently me and him have started to become closer and I've sort of got small feelings there for him. However, my best mate and him aren't on good terms and I don't want to ruin an already good friendship over a boy, but on the other hand he makes me feel so special and sounds like a genuine guy. I haven't spoken to her about it because I don't want to rip our friendship apart. We go through times when we are like sisters and always together and then drift apart but always find a way back to each other. So what should I do? Feel free to comment thank you