... and I've looked everywhere.

He was my companion right after going to the institute, and he appeared on the rooftop with the others when I pushed the button and blew it up. Then he seems to have disappeared? I have looked around the Mass Fusion building and fast traveled to all of the recent places including Railroad HQ.

I can tell he is still a companion because I tried to get Dogmeat to join me to no avail. I also have Lone Wanderer perk and my carry weight is the same as if I have a companion.

Or is this a bug? Any help would be appreciated.