I found Neil, and even though he said he'd be at his shack he was like pretty much all the way up Black Mountain. Anyway, I have Boone with me and when I select Neil to follow me he says "Do whatever you need, I'll be right here." So I'm thinking this is him telling me to let Boone go so he can be my follower. So I tell Boone we should part ways (  :'(  ) and go talk to Neil again but he says the same thing. Any tips on getting him to follow me? 
 
Edit: Wait a second, is Neil even a Companion?

neil is not a companion.  he doesn't even follow you up the mountain.  he runs ahead and waits at the last stretch.  his only purpose is revealing the last three nightkin on the road after you talk to him further up the mountain.  

I'm not sure what you're doing wrong though.  keep trying.  

Was this after you encountered him the first time and asked him to team up with you to take down Tabitha?
 
If so, this is a known bug that hasn't been fixed yet, there is know why around it.

He is not a companion and isn't very useful or key to the quest anyway.

He didnt do shlt... I was fighting a bunch of mutants 3 feet away from him and he just watched

I met him and he said he would be higher up the mountain but I never seen him again so I dont know what happened beside Raul is in the prison at the top so take him.