Hi rose, I'm not a doctor but I have seen both parents with dementia of different kinds, plus my sister's brain deficits after a lifetime of heavy drinking, and a lot of what you're describing sounds familiar. Points I picked up on were:
The way he dresses
Breaking down of social inhibitions
Not noticing something is dirty
Memory lapses
Nothing is certain without assessment at a dementia clinic, so if he will agree with that, I would take him to the experts. Not that they can say why, but they can assess how much and give you an outlook.
It used to drive my sister crazy that when Mum was seeing a doctor she would perk up and put on such a good act that they would never guess she had dementia. Dad used to do that as well, except it annoyed Mum back then. If the doctors aren't taking you seriously, that could be the reason.
Who knows whether alcohol abuse is the sole cause of his problems, but it surely never improved a situation. He might be succumbing faster than he would have if he'd let a different life.
Take care of yourself and don't forget to plan for the future where you can give yourself some respite every now and then. It can be very hard for carers, and you need to look after yourself too.