This man hasn't done anything wrong yet. They are just fuck buddies and he hasn't mistreated Jooin at all. The problem here is that Jooin is catching feelings and he has to hurry up and clear things up with Yahwi. And about that Cain guy, BACK OFF
Catching feelings is always the problem. I think a lot of people just connect with Jooin in a sense that they had the same experience. Having you heart flustered, broken and lost is the worst - so that's why they are cheering for Jooin by hating Yahwi.
And having Cain would be a good mix to the series. He seems to seriously like Jooin though
He and Nohae share a braincell seriously...
It’s Nohaes turn to use it in this chapter
Mom says it's my turn to use the braincell.