Ok so first of all you need to be nice to him because he is still adjusting to his new school.
but i agree its been a while and he doesn't seem like he is adjusting still.
i would talk to him nicely and explain, "we dont really have that much in common anymore" .
and he should understand that and make new friends.
stuff like this is never painless it can hurt him, but you have to tell him.
if you wanna talk more pm me