I'm hoping that he gets some character development, because it seems like they've given him a reason for how he's acting towards the 2nd prince, but that doesn't mean he's going to change... Hopefully he changes. He seems to have a complex about his (seemingly terminal?) Illness and the idea of being replaced when he dies. Hopefully he'll see that the 2nd prince isn't even competing for the throne and will begin to treat his brother right. Having a brother there for him could help him handle his sickness emotionally, but I'm not sure whether this will go there.
He's probably gonna die from his weak health broken then oof
Awww. I actually prefer the first prince to be nice. Or something like he'll have character development. I'm bored of these stories where the first prince will be dethroned in the end and the abused illegitimate child take the throne instead. Hoping for the FL and ML to be free of high society where they were criticized the most. They need a break from them and live happily in a free place