'Blame' or 'fault' makes no difference whatsoever to any financial arrangements or settlements.
If they have not been living together for years she has already left him, surely.
She can divorce him without his consent after five years' separation, or after two years with his consent.
He could divorce her for adultery, and you would not have to be named. Those days are long gone.
But as I said, it won't affect her financially.
Unless she is hoping to be maintained by him whilst living with you?