That poor guy is the sort of person that needs to be appreciated in the industry - who will do back-breaking work without complaint, which a lot of kids these days can't handle.
Personally, that guy must either be ridiculously kind-hearted, or the BO has something over him, whether it be his legal status, or perhaps he is desperate for money. I can't think of anyone who would put up with that sort of treatment unless they had no choice.
I'm glad you're changing barns though, OP. Is there any chance that you could drop hints that you're leaving because of how they treat the staff?