He already has a character development, all along you see the protagonist having pangs of conscience and this since the episode 13. The summit of pangs of conscience is in the chapter 33. From the chapter 35, he is so exhausted that he is almost giving up on the painter but the blushing gives him hope. Actually, I wrote so many analyses more than 50 about him.
My theory is that he was raped, sold by his own father in order to survive the purge. He cut ties with him in order to ensure that his son would take the whole blame. Remember that he ran away to the countryside. However, because Seungho was turned into a sodomite by his own father (to ensure that he would never be connected to his son), the eldest son chose to become the biggest sodomite in order to hurt his father, to let him remember that he was the cause for his misery. The replenishing medicine was used in order to be able to sleep with men. Seungho was forced to become a homosexual in reality. The author retweeted my theory about Yoon Seungho

I read this story for the first time today and I just want Nakyum to be happy in the end, it's so sad to see him like this ;; I hope Seungho have a character development soon, and fck the teacher and Jihwa, I hate them