My DH was paranoid-schizophrenic for many years and he too thought everyone, and sometimes even I was plotting to kill him.
All I could do was offer constant, loving reassurance that they were not, that I was not and hope that a lucid moment might come when he believed me.
As it never did, after 11 years, when I saw it was affecting my children, I decided to leave for their sakes.
It is unbelievably hard to leave the man you love when you can see he is suffering.
But if there is nothing you can do to help or change things, and no 'authority' is prepared to help or support either, what's the alternative?
Not quite your situation Luckygirl and of course you have to choose your own route but I do feel for your heartbreak, having gone through it, albeit in a different way.