Nice Surprise.

Probably both but I am leaning towards the provocation of chasing after Sir.

He feels like NK ran away from him but couldn't wait to run straight to InHun. And SH has already been very clear to NK on how far he will go and how much he resents NK's feelings for Sir.

Do you think so? I think that from NK point of view, Seungho used Inhun as leverage to threat him and out of being mean, mocking his feelings but I don't think he realized until now that it was jealousy.
I don't think Seungho openly said to NK that he was jealous of Inhun even because Seungho himself didn't realize yet (in the blowjob scene he is getting pissed with NK lowering himself to save Inhun and he starts to remember NK drunk confession to the teacher and thinks to himself: 'Why am I so angry?' ) and then mocks NK's feelings for Inhun and the blowjob comes out of pure anger and jealousy: "Whenever Inhun is mentioned, you act as a silly mutt that doesn't know its head from its tail" Were you not intending to protect your good sir with that lowly body of yours"? ... he is seeping with jealousy and the blowjob is his anger but I think Nakyum only sees Seungho mocking him out of mean streak.
He probably feels that Seungho despises Inhun but I think up until now with a defeated, bitter and almost whining Seungho asking 'why do you like him so much' that Nakyum sees that Seungho is actually jealous of his attention to Inhun and that's why he looks so surprised. I think he took Seungho's animosity towards Inhun only as a mean thing Seungho was doing to torture him.
Anyway, I think that even if NK had an idea, now it should be clear that Seungho envies his feelings for Inhun.

I am in complete agreement that NK didn't see any jealousy as the real motivation for SH's hostility towards Sir until this latest chapter. SH didn't woo him, he took advantage of him while drunk and then violently forced himself on him. All he expects from SH is a nobleman walking all over him.

And I also agree that NK could only see it more as SH being mean to him based on all his experiences with SH so far.

But NK is also becoming aware that SH has acted out of the norm around him. Whatever he took out SH's confrontation with Jihwa it was still done for NK's sake (NK a lowborn was put above a nobleman from any outsider's POV. Even if NK was the victim, it wouldn't have matter because a nobleman was the victimizer). Medicine is extremely costly and from NK's POV SH is just mean to him so he wouldn't feel guilt for hurting him, so why waste money on him? Why personally carry him to SH's room because it is the warmest? Why would SH inconvenienced himself and surrender his comfort to NK?

However, my response was based solely on SH's point of view as he is the one that utters that NK never learns. To SH, he couldn't be more clear (he is not the most rational person when it comes to his feelings) to NK but Nakyum just wishes SH would leave him alone.

And this is not to say that SH thinks he loves NK either. He is not even there yet. He just wants NK to the point of distraction. SH knows he is jealous of Sir and finds it a slap in the face since he sees right through Inhun (I mean honestly only NK and small children can't) and knows he is not worthy of the devotion NK holds for him.

This more of their awareness period.

That's why I think SH dropped it when NK didn't know how to answer him when he asked him why he liked Inhun. I think they are both starting to get an understanding of each other.

I love your analysis. I can see what you mean and it makes sense. :)