This must feel very unsettling to you.

You are describing delusion. When someone holds an irrational belief despite rational evidence to the contrary. Please check the definition of "delusion" for further info.

It's not unusual for delusions to be mixed in with rational thinking and behavior. Sometimes delusions are limited to a certain topic or event. One's thinking can be partially delusional.

Is your son seeking help?

Love to you both,
WC