I need some advice, help me please?

so this guy in my cl likes me and i do NOT like him like that because A.) hes my friends B.) i like his best friend. Well he asked me out and I don't know what to say? I mena this guy really likes me and when i say no and he asks why what do i tell him? Sorry i dont you like that can you hook me up with your friend? Any advice please and thank you!