Clearly hasn't read harem before otherwise they wouldn't say that. In real harem stories, most girls don't even have reasons as to why they'd like him and may not even know him before jumping his ass, not caring about boundaries or whether he might have a gf (lk wtf) just saying "I don't mind sharing". As of today's chapter, only Nayeon really likes Hajin and the 2 others - good feelings (which is normal when the said guy has helped you on multiple occasions). I can't speak for the novel so I don't know if this will head in a harem direction in the future, but as of now, there is no such thing! Which is why I continue to read it cuz I'm not fan of harem.
All of the others need a big incident to happen, then Mc will break of with them going no contact for them for those guys to start using their brains a bit before giving a dumbass apology after a month or so.
Here you could see Taejoo had remorse way early on, even deciding that he needed to change himself and correct his actions towards Euihyun, trying to go out of his way to support him constantly - especially during the worst time when he gave euiyoung baby away. And only after all that did he ask for an apology. Euihyun hasn't completely forgive, but he did think he could trust him, because of the way he was treated by him, unlike other Mcs who expected to forgive the ml after one apology
This will of course not change the fact that Taejoo did him so wrong in the beginning. And the trauma he put the two brothers into. But he's made the most effort I've seen from an ML