Y'all need to STOP TALKING SHIT ABOUT THE SEME! He acted like that toward Hosik becuz... maybe this sounds like a spoiler but the seme is very protective of the uke because in the past life, Kim Hosik and Lee SeoYoung are a couple in their past. in the past even though they were a couple but they cannot enjoy their time together as in this life where they can walk together in public, make love in public, hug and others because of their status. In the past, Hosik was born as a servant in Lee Seoyoung's family, and Lee Seoyoung in the past was a young master of a high status family at that time. they both from childhood to adulthood are always together until finally they start their relationship secretly from Lee Seoyoung family's. they both know if they can't be together forever but what else can they do, they both love each other especially Lee Seoyoung who really loves Hosik. but even though he loved hosik with all his strength he still could not protect hosik like he did in the present time. Until there comes a time when Lee SeoYoung has to marry another woman in order to have children, Hosik who is only a servant can only sincerely see Lee SeoYoung getting married and having a child with another woman but Hosik is very fond of Lee Seoyoung's son. The time came when Lee Seoyoung was on his way out of town to take care of his family business, Lee Seoyoung, who was out of town, didn't know that Kim Hosik was seriously ill. When Lee SeoYoung returned home, he found that the hosic disease was getting worse and his death would soon arrive at any time. Lee SeoYoung rushed to the hosik's room and found hosik lying limp like almost died then. he immediately ran to hug hosik and cried, hosik had opened his eyes but before long he closed his eyes and hosik finally died in the arms of Lee SeoYoung, And that's when Lee Seoyoung felt a deep sadness until his long hair that he tied was loose and disheveled. he kissed the hosik who was lying dead, in front of all those who witnessed it. So in my opinion, Lee Seoyoung's character who in this present time is a symbol of his repentance will regret from the past where he could not make hosik as his partners, could not protect Kim Hosik, and could not give happiness to hosik although the way he does all that is wrong and looks manipulative, overly protective, childish etc. but that's the way he vented all his affection that he couldn't give to hosik in the past. That's my opinion.
Hosik's story