Well that's a brave post, and I'm sure that you are not the first carer who has been in this situation.
I'm not married to someone who has dementia, (and early onset dementia as a partner must be particularly devastating..) just experience with someone I loved, so I'm probably not the right person to comment, but here goes., I have two points to make.
Somebody mentioned previously about the guilt that carers suffer whilst having to make decisions about their loved ones. Starts off with the little love lies, notes to the doctor that they can't see, talking about them behind their back on forums...... Life is difficult and you may have to do things that will make you feel disloyal and treacherous to the person you love. It doesn't go away even when they are dead. I just wonder that if what you are doing is going to make you feel so much worse in the end.
Second point is that although you know that OH is a vulnerable person with his illness, you must realise that you are disorientated, sad, lost and thus vulnerable too. Having a good old friend that you can talk to and understands and sympathises is a wonderful thing, but a friend should be looking after you, not taking advantage of you in your hour of need.
Living with someone with dementia is horrible, and maybe you should think twice before you complicate your life even more... Gin works quite well .... XX