He was afraid Sunhwa would find out he had something with Mokyeon because he still likes Sunhwa, and although he got along with Mokyeon (for a brief time), Nanjo still said he liked Sunhwa and was doing everything he was doing for Sunhwa. I think the author is trying to show (through Nanjo’s conflicting actions) that he grew to like Mokyeon a little bit but is in really hard denial. And even though he likes Mokyeon, he still treasured his relationship with Sunhwa more because he believed Sunhwa was genuinely a nice person. Which is why when Sunhwa finds out that Nanjo slept with Mokyeon, and left them, Nanjo left Mokyeon too (as seen in the most recent season).
Thank you so much for replying to me and answered my question. But, was it shown how, when, or why Nanjo like Mokyeon? What did he see in him? Because there was a reason why he likes Sunhwa. I just couldn't imagine how he came to like him when the last thing I saw (earlier chapters) he was disgusted or hate Mokyeon for doing things his way. Like they were not getting along at all. I understand why he would be in denial, after all their relationship didn't start on good terms. Again, thank you for having this conversation with me. I just couldn't bear anything that was happening so I dropped it and I couldn't read it now. There was so much tension. Thank you so so so much.
After Nanjo gets “used to” sleeping with Mokyeon, he starts to treat him better. He smiles at his silly text messages and starts catering his whims (like buying him a gift when he asks for it). I don’t know exactly what he likes about Mokyeon because we never see his thoughts, however the author said we would see his pov this season so maybe we’ll learn more. I would have to reread to explain in more detail because it’s been a long time since I last read this but I remember Nanjo starting to become more comfortable around Mokyeon before he fucked it all up at the end of the season due to his jealousy. Also no problem! Despite how horribly this manhwa started, I kept reading because the character dynamics were interesting. I like how the author shows so much emotion through Nanjo’s actions despite him being very poker faced most of the time.

So, I dropped this ages ago when Mokyeon still blackmailing Nanjo. Y'know the start of their deal and he kept on forcing himself on Nanjo even if he said otherwise. My question is how, when and why Nanjo fall for him? Sorry. I don't want to read, but it's my curiosity kept on bugging me. I just don't understand. And if someone of you were kind enough to summarize the S1, I would really appreciate it. Cause after I dropped it, I jumped on the S1 finale when Mokyeon f*cked Nanjo in front of Sunhwa even if Nanjo kept telling him to stop. To me it looked like that Nanjo didn't really wanted to, but Mokyeon kept on pushing him. Even on the part before that when Nanjo avoiding Mokyeon. Nanjo was afraid of being found out by Sunhwa that he had something with Mokyeon. Why? If he truly love Mokyeon, shouldn't he stop seeing Sunhwa? It's not like he was actually protecting him when Mokyeon keep using that as a reason to prevent him from leaving him. So, yeah. Thank you in advance if someone would answer me. (▰˘◡˘▰)