I don’t know what to do :(

I’m talking to this guy and he’s 18. The only problem is I’m 15. Three years isn’t a big difference butttt since I am 15 and he’s 18 it kinda sucks cause ya know, it’s illegal🙂. I know this guy pretty well cause he’s my cousins best friend and he’s super nice and funny and definitely more mature than ppl my age. We definitely haven’t done anything bad but I am catching feelings for him and I don’t know what to do. Also he had feelings for me too but he’s scared to tell my cousin/ his best friend cause he’s scared my cousin will get pissed. I haven’t told anyone about my situation so I’m hoping you guys can help. Please no judging😭