I fully understand your feelings. My husband has a diagnosis of Alzheimers and is in denial- this makes my life difficult . He often refuses to attend appointments or to join the family for a get together. I find distraction my best option, if I change the subject and try again later that often works. I think you are well advised to see his GP to discuss your husband's situation. Having POA should make that easier for you. He may or may or may not have dementia, if he has, no amount of trying to reason/ argue with him will help!! You will never win . If my DH won't take medication , a tablet box with times and dates would not help !! If he digs his heels in , I have no choice but to accept that , keep calm or suggest we have a coffee or a short walk. That often works.
Please make that appointment at the surgery , there are many reasons for your husbands behaviour so speak to your GP ASAP. I have empathy for your situation and know how frustrating it is when you are trying to reason with him and get nowhere. Good luck and although it is difficult try and distract your DH rather than try to press a point - that is a fruitless exercise and only serves to distress you.