Your husband may just be undergoing paranoia if theres been any times of stress or traumatic experiences(including a run in with someone who took place during a traumatic experience) could have your husband in a prolonged state of depression. With depression comes paranoia in some cases. Psychosis is when hes become out of touch with reality so if he begans to act disfunctional and behaving innapporpiately or weird at random times where hes in a state of confusion about rather people are real or life is real then those are early stages of pshycosis. I suggest taking him to therapy not like marriage counseling just regular CBT counseling. If you have suspiciouns of him haveng Alzheimer's i suggest going to the doctor for testing.