Responses
You really should read the novel if you are confused by this "sudden" change. Even in the manhwa, there have been clues for a while now but the novel goes into things even more in depth so you can see that he is having an inner struggle within himself because he is also confused by these feelings that he is having. That's why you can hear his thoughts about not minding that inseob was holding onto him even though most of the time he doesn't like others touching him.
Okkkk everyone complaining about the eng translation, but my problem here is why the fuck does he suddenly changed?!? Just because of that night??? Like is he a transformer or sailor moon? I mean....I thought he'll have progress wherein he realizes that he cared about inseop....