Mgue, this must all be so difficult on you and your fiance. Hopefully the drugs will calm him down some. It must be difficult but you really need to act very "matter a fact" when you are leaving him so he can pick up on that energy.
Ancientgirl used some drugs to calm down a stray that she was trying to integrate into her pack. It seems to have worked as the cat can now roam in the house without killing anyone.
that you have the same success with Ozzy.
A bit more patience and I am sure it will work out fine.