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I am afraid that your husband has a very serious mental disorder. At the very least he has Paranoid Personality Disorder, but more likely it is Schizophrenia, Paranoid Type.
His delusions are very strong and he is beginning to become a risk to your life and others because he is sleeping with a loaded gun and he may very well kill you or someone else, not for a rational reason, but because he is psychotic. He is very dangerous and needs to be treated and stabilized.
Unfortunately someone with paranoia will not trust anyone to treat them and will not believe an expert or take medication (which may be poisoned, in their minds).
He could be stabilized with antipsychotics, but the only way you can get him help is to convince a judge to commit him for observation and possible treatment (which may only be from 24 to 72 hours at first, but he may be committed for longer after a report is filed).
This is a painful situation for you because he is the man that you love. However that will not protect you from his psychotic false thoughts. If he thinks that your 21 year old nephew is an evil culprit, then that boy is at risk.
If someone comes to visit it might be misconstrued by a mind that is no longer sane and cannot work logically.
IF he can start a course of treatment, his paranoid delusions can be controlled, in many instances, although if this is what is wrong with him he will have to stay on medication.
If he is treated and the delusions stop, then he has a chance at a very normal life.
If not, then the possibility of a tragic event is a very large one.
I suggest that you talk with your family doctor and with your attorney as the next step to take. This is a volatile situation and you must take it very seriously.
I am sorry to give you such a painful response, but it is my duty to tell you the truth and warn you of the possible dangers, which you probably are already aware of to an extent.
I shall keep him, and you and your family in my prayers.
Please get the help I suggested and stay safe.
Elliott, MAE, LPCC, NCC, CCMHC