Well in my opinion i think in the book the duke really loved her and when she died bc of unfamiliar sickness he tried to treat her with the saintess's help but she couldn't treat her so the duke was so mad that he kidnapped her or smth and became crazy cause his beloved wife died u know in his last moment he said "i just wanted to live happily with her" meaning his wife tbh he's not even the second ml ㅜㅜ it's just my theory guys, it's not kind of spoiler or anything
I am not simply living to read manhwa im reading manhwa to live
could be because of the self-hatred she is/was an unreliable narrator. What she described as "unpleasant expression" could be him shocked/surprised that she would want to have a child with him - for somebody who hates themselves like obviously OG Grace did, it's common to misinterpret people's compliments or words as mockings and insults - even when the person did not mean for it so.