He do ended up living a miserable life, just not on screen. Personally feel its, kinda useless to see him struggle tbh, id rather have the screen time for the main couple. He deserve meaningless, empty, lonely life far away from the thing he desire, just like his father but better cs now he only have the fraction of privilege that enable his mindset. Pathetic then even worse at the end.
Beside, story wise I dont see any way he could repent with his memory still intact that does not put darling on potential danger and trauma. His obsession and entitlement is an integral part of him that wont be easilly stripped down. At least not without writing a whole several episode about him. The story is ultimately about class divide and the struggle that the common folks face. I feel adding more narrative breakdown to him would shift the focus of the story.

Beautiful story. I was left wanting more about them, but they all had a happy ending. As for the brother, although I acknowledge his trauma, I think his ending was too easy.