I like my bff's brother

Ok so I don't know what to do here. I've been friends with my bff and her brother for almost 10 years. I just got back from a trip with them too! So he's 18 and I'm almost 15, 3.5 year difference which I don't think I'd bad, it just complicates things. So over FaceTime when I was with him my dad was like oh youre with your bf as a joke. I explained to him that my dad does that to everyone which he does😒 and I'm actually happy that happened Bc it sort of makes him think of me differently. I don't want to tell my friend I know she'd be fine with it and everything. But what do I do here? He might know I like him which is good but any advice on how to get him to feel the same? We have so much in common that everyone thinks is weird Bc were like the same person, which both of us know too! I have also liked him for a few years now😊❤️