Without the use of PlayerMarried?

Like lets say you saved this slave from a group of slavers and willing to give up your home for this free slave, so that they don't have to go back to the same spot where they were caged up in. Be like a new destination spot. I assume maybe AI Packages will make this work? Or a Faction?

put him in a quest alias with a package stack that keeps him where you want him.

this also makes sure he's persistent so he won't get cleaned up ("a slave" might well be a spawned leveled actor)

edit: ...and adjust his faction settings