Mokyeon is his own worst enemy because he constantly told Nanjo he would get bored of their arrangement soon and even refused when Nanjo first asked they both step back from Sunwha. Nanjo probably felt a sense of duty in regards to Sunwha so he never let himself go completely with Mok, but now Mokyeon admitted his feelings and he's serious about them and Sunwha found out about them so he's out of the picture... Now that these obstacles aren't there anymore I'm sure something between them will shift (hopefully for the better). The problem is that Mokyeon is just assuming that Nanjo doesn't want him too and he isn't asking Nanjo's opinion or stating his intentions, he asks to see Nanjo from afar but can't imagine asking to date him. Maybe the last scene is Nanjo teasing him about it and ask him to speak his mind clearly
This manhwa might not be deep, but it conveyed emotions clearly, i could see throughout the chapters that nanjo likes mokyeon, something is holding him back, probably because he knows mok is a player, you could see it clearly in his eyes,he has something to say but never did! You can see it in season one