I thought the ending took a weird turn at first ,but now, i think it's pretty innocent, like the wolf didn't fully understand what a "marriage" is.
The theme of " to be human" was floating around, wheter it be his flashback , or him raising the girl to be human.
he said " it's the way of people" as if he's trying to be more "people-like",while also trying to imitate the bonds that his role model ,his granpa and granma ,shared with each other.
he wants someone to be his "pair" or "wife", someone who will be there for him and vice versa.
He think that , with "mariage" and "wife", he will be like his parent and that he will be completed as a "person".
Or Atleast that's what the theme/tone of the story led me to believe.
But who knows?
Maybe the wolf really wanted to fuck the girl, even tho it would be contradictory to the theme and tone of the story, and then continued to ruin the whole manga.