What mental illness does this sound like?

My husband is in denial but I suspect a family member of his is suffering with some kind of mental illness.I think he needs professional help and medication.He is also on the brink of losing his job because of it.These are the symptoms:
-He talks to himself. I, family members of mine and his co-workers have seen him doing it.I have seen him talk to himself for up to an hour like he's having a conversation with someone who's not there.He also does it in the mirror.
-He taps on his head repeatedly.
-He act paranoid sometimes and doesn't like people talking about him.He also asked me to check his food a few times because he thinks there's poison in it.
 
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