
Hey, he is a kid who lost both of his parents when he was really young and then the only family that he have left is going to marry, he is afraid that he will lost his sister too, because she will start a new family. It's completely normal behaviour in his situation, he is just a kid after all... ╮( ̄▽ ̄)╭

Not to mention hes in a really stressful situation. The palace people are obviously out to get him and the only one who has his back is his sister. She made sure he got secret books to study do he didnt become a useless historian. She helped him when he got scammed with the pen. She sticks up for him when the nobles are being two faced. Shes more than just a sister she is his litteral support right now.
I cant get myself to like the brother. He's super annoying lmao i kinda wanna slap him and treat his sister the way she should be treated Σ(  ̄□ ̄||)