Just another stray thought (no pun intended, really!), do you have one of those stick and string toys for your cats? Try getting him interested in that, as well. The play time together will help him bond to you. I've seen it work with ferals and semi-ferals before. Just part of the total package you're already offering him.
As for your fiance, perhaps he could spend some time in the same room with the cat, sitting down, preferably on the floor. It's the rare cat who will attack without any warning at all. Ears back, body low, that moaning sound...he'll know if Nero is getting ready to launch an offensive.
As for your fiance, perhaps he could spend some time in the same room with the cat, sitting down, preferably on the floor. It's the rare cat who will attack without any warning at all. Ears back, body low, that moaning sound...he'll know if Nero is getting ready to launch an offensive.