So I was doing "Shoot 'em in the head" and gave the keys to Crowley, then followed him on his spastic route to the fort. We get to just down the hill from the fort and he turns around and starts shooting at me! I loaded an earlier save and followed at a different distance, but the result was the same. Is this a bug? Or does Crowley get paranoid at a certain distance from the fort? What do you think folks?

Think it is a bug, maybe just try kill him

He doesn't want to share the prize with you. So yes, it's not a glitch.

That's what I was thinking, so I fed him six or eight 12 gauge rounds and looted his steaming corpse

This happened to me too, partner. I once was a curious traveler like you and I followed Crowley through all the Metro tunnels, through all the hills and plains, until I finally followed him to the entrance of Fort Constantine.

And he got hostile, up to there. I didn't know why. I wanted to follow him in the little shed, but he didn't go in. He just turned hostile. Although, he was also fighting some of the robots, that were there(Note: I should've gotten rid of the robots beforehand). Anyhoo. If you ever get another chance to follow him, take out the robots at Fort Constantine, beforehand and hopefully, Crowley will enter the shed. If he does, use Chinese Stealth Armor to follow him. (Note: I'd also get the "Silent Runner" perk when following him, in the shed, so he doesn't figure you out, due to hearing you.)