So he is living with you. Rent free?
The adult dc leave in the former family home.
His wife lives in her own home.
As you are financially independent, the only immediate, material way this affects you is that you are subsidising his housing and possibly his food, bills, etc. So if you are not doing so already, I would charge him a reasonable rent.
If I were him, there would be no question of leaving my estate to the wife or to you - I would leave it to my adult children.
Just as I assume you would not leave your estate to him.
He does need to explain his thinking and his plans to you. Like an adult.
Yabu to expect him to get divorced, or to insist on it. That's his shout. Yanbu to discuss how him not being divorced affects you - materially, socially, emotionally - and to ask him to why he is still married and if he intends to remain married. You do deserve an honest and open discussion.
I also think that for your own good, you should get out of the relationship if he chooses not to divorce. Longterm that is not a good option for you, and of course the longer you are together, the more you want to combine finances and futures.