THIS IS NOT A LESSON TO NOT HELP ABUSED CHILDREN.
I think when they were children, he saw Geon as a puppy. Like you just want to be their whole world and such. But human beings are complex and respond differently. I’m not saying that Hyungnim deserves what’s coming for him but he also could not react and raise Geon properly because of the circumstances. Everyone is saying that this story teaches us to not help abused kids let’s be fucking for real. Samyeong couldn’t help Geon properly because of the royal family and it’s not like he actually wanted to leave and get married, it was a command from the KING which would mean treason to disobey. It was already stated that he was only allowed to take care of Geon because the eldest prince was fond of him.
In the real world, there are measures in place to deal with emotionally and physically abused children that does not have to lead to more psychological trauma for both the victim and the helper of the situation. If anything, this is a lesson on how imperial politics turned two perfectly normal boys who could have had a perfectly healthy dynamic into something twisted because of their cruelty. There is a reason why most of the world has abandoned that system because it gives birth to more tragic stories like this.