No doubt Apollonia did accept Michael for what he was She was keen and accepting who he was

While Michael's wooing of Kay may have been bloodless, passionless, I don't think he gave any BS to her.
I reckon it was one of the very few, perhaps the only time he was honest with her, truly believing in what he was saying

While once the Thunderbolt faded, even if Michael had grown very weary of Apollonia, he never would have lost the family

I didn't think anyone other than Vito knew about Apollonia but Kay for someone who was banished, knew a lot of inside stuff even that Michael killed Fredo