hello
@Amber123 and welcome from me too
it's not at all unusual for someone with a diagnosis to turn against the one closest to them (I suspect it's a way of placing the 'blame' for the feeling that something is not right but not being able to rationalise what it is that is wrong, because it can't be them, they are fine)
a divorce would very much alter your situation and future, I am wondering how you feel about all that it would entail
if a solicitor is doubtful that your husband has the capacity to understand this decision, I don't think they would proceed
I do think you need legal advice and some solicitors will offer a free initial chat .. maybe one who deals with 'elder' issues may have some experience of situations such as yours
this site might help
https://societyoflaterlifeadvisers.co.uk
PS having just read your reply above .. it may be good for both your husband and the woman concerned if you did raise your concerns with the Local Authority Adult Services
and it may be wise to look to your own finances, to have your own accounts