I wrote this at chapter 4, two years ago:
While he fixed how he interacts with his fiancé, he still incorrectly believes that the "epic" was written as a documentary, and still not realizes that it was simply pro-Wilhelm propaganda.
She may will return after they clean up the mess of house Allingham. The decision will be up to Carol, as the duke takes in those who did not choose to stay in the Allingham domain. As I see, all she needs is a permission (and tickets) to regularly visit her sick mother.