Aww, I was hoping for a BL lovestory blooming at the side between those two where they initially bickered and fought but eventually fell in love as they grew up...but it seems they're falling more and more for Lippe as time goes on and not each other.
But yea, I agree with the others, I'm starting to have second male lead syndrome. The duke's heir is kinda creepy and weird. Hildert would make for such a better ML. She is even raising him and molding him to become the perfect man for her.