I’m friends with an antisocial autistic kid against my will.

He is around the 200-215 pound range and is about half a foot shorter than me, he never stops talking about shooting up the school, anti-semitism, racism, jerking off to hentai, or about tower defense simulator. He’s invited me to a discord server and all he posts there are porn and YouTube shorts. I can’t befriend him because I’m literally his only friend. But if I keep being his friend I’ll probably be associated with something horrendous because he won’t stop talking about his plans to shoot up the school or about his plans to rape a girl. How the hell do I manage to pry him off?