In-Hun had the case of CLOSET HYPOCRITITIS , he knows Na-Kyum has feelings for him but he is the guy that says NO TOUCHING THE LOW QUALITY SUBHUMAN PEASANT ╮(￣▽￣)╭
He must hates the both for different reasons, and seeing them interacting like this just upsets him even more...
That is very true, but I'm just making theories on why that is I suppose? Something that is more so internal that makes him this way. Haha and yeah that's basically him 100%
That is true, but I wonder about that? Is it really hate or jealousy? For Seungho to have power, be openly gay and have money (pretty much have everything given to him). As for Na-kyum a low born who was originally seen as some "talentless" idiot- He actually has genuine talent for art and is very much noticed by others for that reason. I mean he sold his art to make some bank to survive and now he is with someone powerful as Seungho- That would make sir in-hun very jealous tbh.
Sir in-hun has no actual skills that are really note worthy (other than archery) and being able to plagiarize other works. (Yeah it may slip past /some/ people but it's not going to get him very far with that tbh).
Sure you can say its /just/ hate, but I feel like its something more than just that. And jealous is definitely there imo.
I'm agree with your analysis of the characters' background and situation.
About your question I think it's both, hate and jealousy mixed with other feelings of frustration. Also In Hun surely is getting really upset after what Seungho did to him (makes him kneel down); and seeing the both Lord and Nakyum being all flirty must be frustrating and annoying to him.
*******
*************
*****************
********************
***********************
In this chapter (23) we can still see that Na-kyum does not remember a damn thing (just a vauge face) and that's it. But with Seungho teasing and really trying to earn Na-kyum's attention is really cute here. But I do wonder why does it seem that Sir in-hun is jealous of them interacting? I wonder if his homophobia is more so internalized rather than it just being something he hates just because. Does Sir in-hun actually like Na-kyum but can't fathom being gay in any shape way or form maybe? He must be feeling some type of way for him to sit there looking mad tbh.