My cousin kissed me ..

Ok first of all.. ITS SO WEIRD my uncle ( my dads brother ) his girlfriends brother.. I’ve known him forever but he’s my cousin blood or not!! Idk what to do. We’re both 17 but if I tell my uncle or anyone at all they will kill him I’m just so weirder out I needed to tell someone ( we aren’t blood but still weird !!!) he’s been saying hes had feelings for me since june.. I need advice.. do I just distance myself? Tell someone? Tell him something? Please ):