This is some of the most palpably intense chemistry I've seen in a BL. I think it's largely due to the fact that, somewhat uniquely in manhwa....both characters are really fighting with their attraction to each other, and spending a significant amount of time building a relationship that isn't anchored in the physicality.
The attraction from each of them - and their distress over being into someone completely unexpected - is so different and so effectively conveyed.
Jaeyoung had already held some level of attraction to Sangwoo from early on, and he's also not particularly bothered by his sexuality. He's pretty fluid, and while he hasn't dated or been romantically involved with guys in the past, the physical side isn't new to him. So he's more torn up by the fact that he's increasingly invested in Sangwoo - not just wanting to tear off his clothes to see what's making him tick underneath, but genuinely finding his personality strangely adorable, despite all the difficulties.
Sangwoo, on the other hand, has a very clinical idea of sexuality, which is to say: he assumes that one day he will fall in love, get married, and make babies, just as his parents did, and like any normal human being would. It's not that he's appalled by homosexuality on a moral level - he just doesn't understand the point of it, since biology and sexual urges are in place to spur procreation. Which you can't do with two biological males.
So when his body responds physically to another person for the first time ever - and that person is a man whom Sangwoo had been assuming he hated - he completely loses the ability to function around him.
This leads to a couple of decent scenes where Jaeyoung gets frustrated/hurt/offended by how strongly Sangwoo had reacted, and ultimately removes himself from Sangwoo's life, determined to get over him.
Sangwoo, however, likes being around Jaeyoung, and finally starts accepting that to some extent, becoming the one to approach Jaeyoung again and insist that they resume working on their mobile game together.
In the process (and through some social media browsing), he discovers more about Jaeyoung's family, personality, and interests, and gets more and more attracted to him, to the point where he even kisses Jaeyoung when he assumes he's asleep.
This volume ends on a note that in other manhwa would likely steer into kind of dubious territory, but Jaeyoung is honestly just...so good with Sangwoo. He's learning how to be patient and deal with him on his level, with things like announcing when and how he wants to touch Sangwoo, and giving him enough time to leave or stop him if he really doesn't want it. It's such a nice indication of how closely he's paying attention to Sangwoo and how much he truly likes him for who he is.
So yeah, still enjoying this quite a lot. I'm curious how similar it is to the novel, but right now, it's making me want to rewatch the live action!