I strongly advise getting out.
What worries me is this delusion, that all RH negatives are evil. How will that pertain to you if you try and leave?

Will he believe you are now one of "them"?
Will he come after you, believing you know too much?

Your in a potentially dangerous situation with someone who is either delusional or a fantasist, he has already shown he is unstable if his beliefs are challenged.

I am curious as to what keeps you with him, or why you stayed once he began to reveal these paranoid beliefs.?

He is either very ill or very lost and I would think being in a relationship with him could become incredibly scary quite quickly if his belief that he is being persecuted takes hold.
Challenging him with logic is pointless and only likely to antagonize him and push him deeper into his beliefs.
He needs treatment, but I can almost guarantee he believes that treatment is the government or his enemies trying to brain wash him or kill him off and replace him with a clone or something.

You are at very real risk, if your blood becomes the focus for his delusions. You can't argue rationally with him, you can't shake him out of this.
Nor is he suddenly going to wake up and realize how absurd it all sounds.
He has a community online that believe the same things he does and that's enough to keep him fuelled.

His losing his job is what sounds like the beginning of a downward slide into instability. Along with the keeping secrets and erratic behavior.

Have you been to his employer to ask what happened?

I have no idea what your options are as far as intervention goes, but I suspect until he hurts himself or someone else there is nothing the authorities will do.

Does he ever step outside this belief system of his, or is it a 24/7 thing?

I am guessing it's probably the latter.

I strongly advise you seek professional advice for yourself as to how to extricate yourself from him without him going postal.

Does he have a history of violence or aggressive acting out?

Whatever you decide to do, even if it's stay with him, please seek some professional advice on handling him.safely if that's possible.

All the best.