@Danear I would say its different. There has been basically no effect on his mental state throughout and he can really do whatever he wants, but does need to put on more of an act around the village. Its more of a type of play they are doing at this point, lol. Everything they have done is consensual and there hasn't been really any abuse aside from a few physical gags. The only thing left typical of Stockholm Syndrome is that she is technically his captor, but he never really perceived their relationship that way. It should also be mentioned that he could leave at any time by storing his collar and digging away.
There are a lot of isekai with slave characters who have this tragic past and when their owner (often a young male from Japan) treats them like a person (or beast-person), they open up and become absolutely infatuated. In many cases, the owner maintains the slave's status even if they could easily free them. Personally, I find it a bit gross, but I don't really get that impression here.