Telegran, first of all, welcome to Gransnet. Second, I commend you for sharing and hope this is the first step towards improving your life
Narcissist, threatening, abusive, controlling bully with violent tendencies; he makes a tense atmosphere within your home, isolates you from friends & family and intentionally cuts off any means of escape or relief for you - your husband shows all the classic signs of being an abusive husband that is potentially very dangerous. You say you have already had to have medication for anxiety and it sounds like his constant put-downs, threats, verbal abuse contributed or was the main cause of this. Your home is somewhere that you should be able to relax, breathe easy, feel safe and secure, be able to invite friends and family round for company, celebrations, meals etc - it should not be his personal battleground. How long before he starts carrying out some of his more extreme threats? Abusers do not stop, their behaviours worsen. I hope you can keep yourself safe whilst working out what you want to do. Anyone who has experienced any form of an abusive partner/domestic violence and got out of that relationship is likely to advise you to leave him or get him to leave. It does not sound like dementia, it sounds like abuse. It never ends well if he is allowed to continue his utter domination and he will not like anything that impedes his 100% control, but the priority has to be your physical and emotional safety.
I agree with other people that have posted not to worry about your elderly mum as she would almost certainly want you safe and well, out of harm's reach, and happy. However other people might be affected by decisions you make can be dealt with at a later date - right now you need to focus on your needs and make some tough decisions. Abusers rely on secrecy, on their targeted victims keeping quiet and internalising everything - this is a big part of why so many people have these problems over longer periods of time.
I can't reiterate enough how important it is for you to be aware of your personal safety. Know that Gransnet is here to support you, prop you up when you are down etc. Please take care of yourself, if you have any friends or family you can trust then reach out, share, unburden yourself and accept their help. I know I will be thinking about your post and worrying about you. Be careful, be safe, be yourself and be happy. Best wishes 