Sue.Mia's Favorite

It has to do with the purgery that happened many years ago. Every family around Yoon family got punished. In my opinion, at that time, the father asked his eldest son to take the blame in order to divert attention. In the beginning there is this rumor that SH was chased away from the family after his father cut off his son's topknot which is a grave humiliation. He was punished by his father for sodomy. That's why SH told his younger brother that he is living by his father's principle. SH might not have been a sodomite from that start but was forced by his father to be one. This would explain why he doesn't hide anything... On the other hand, it looks like SH had problems with it (SH gets replenishing medicine). Jihwa even said that he had to prepare him before he could get aroused. Only with the paintings he didn't need help anymore.

All this would explain why
1. SH is actually an educated and intelligent lord (he has a lot of books in his library and he read them all, he could recognize the lact of talents of Jung In Hun.
2. he is resenting his father. Due to his father's action, he couldn't enter any function in the administration and had to take the blame in order to save his father's reputation and family.
Let us not forget that all the servants were replaced, after he left his father's house. And this shows that the father was somehow involved in the conspiracy and they erased every single trace.

Maybe he had to witness all the killings and was only able to save one servant. SH has mood swings and he has trouble to sleep which means that he must have suffered a lot in his past. Imagine if SH's reputation as sodomist was created by his father...