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I-

Oh jeez, you really got a problem with Chungyeon. Chungyeon is pure and polite. One of the few women in her work wants to befriend her, naturally she goes for it. Why wouldn't she, huh ? How can she know that the manager is a manipulative batch. Knowing that homosexuality is still taboo in Korea, she won't suspect every girls being lesbian. By far, when she's with Chungyeon, the manager has been friendly, she's "only" creepy offscreen.

And Chungyeon doesn't have lots of female friends beside Chanmi who's very tactile with her. So she doesn't see the problem with the manager wanting to go out with her to eat something after work, or suggesting eating something together during the weekends (Chanmi acts like that with her to the point that when they were in high-school, their classmates joked about them being a couple) and as far as we know, Chanmi doesn't love Chungyeon romantically.

The only one who got a problem here is the manager. Forcing herself into Chungyeon, knowing she's in a relationship and Chungyeon won't fall into her trap and kiss her because (like I said before) she isn't a pushover and she loves Mai deeply.

I'm going to say it again, Chungyeon isn't the one to blame, she isn't weak enough to cheat on her girlfriend whomst -and the author made it very very very very clear- she loves to the moon and back. The manager is the only one fucked up in the story.

I don't believe Chungyeon is stupid enough to not understand what's going on.
Yes, first she says that she wants to go home and knows that Mai is waiting for her, and then she goes to eat with the Manager, in fact choosing what is more important to her, at least because of her excessive politeness and spoils the relationship with Mai, who is already going through a bad time. Just like when she says she doesn't drink and then gets drunk. This is in addition to the fact that Chungyeon really coldly communicates with Mai.

And as for the kiss, something is going to happen at the end of the season, and looking at how Chungyeon is acting, I wouldn't be surprised if she really goes for it, especially if she drinks again. And I didn't say she was weak, but she's easy to manipulate.

But even if this does not happen, there will still be some kind of misunderstanding situation when the Manager will arrange everything so that May would leave her.
And looking at the end of Chapter 59, it becomes clear that most likely Mai will go to her home and not warn her, well, see her with the Manager.

The Manager is not the only one who has screwed here.
As I said, Chungyeon is too naive and polite, which makes her easy to manipulate, and she can't talk to Mai or even understand what's going on with Her.
At the same time, Mai is silent and doesn't say anything when Chungyeon decides to move because she doesn't want to hold her back, although it's obvious that She didn't want to let her go. They all screwed up.

Again, Korea is a pretty conservative country so encountering gay people isn't "common". Plus, the manager's moves were very friendly and too touchy buy nothing alarming in Chungyeon's point of vue. But she got taken back when the manager was telling her she wanted being more than a "sister" to her. I think that's when she's going to suspect the manager trying to hit on her.

As for Chungyeon "choosing" the manager instead of Mai, you read the chapter wrong. Someone messed up in the work, loosing some of the company (important) data so all of the workers need to work overtime and the weekends to restores the data. So Chungyeon can't go home to Mai. Chungyeon and the manager went eating chicken after work (I think it was Friday), so again she didn't choose anyone. There's nothing wrong going eating with some co-workers after work.

Chungyeon and Mai already communicated about the whole "getting drunk with the co-workers" and they've already got over it with Chungyeon promising Mai she won't get drunk again.

The big problem in Mai and Chungyeon's relationship is Mai's lack of self-confidence, her last relationship destroying all her confidence. I'm pretty sure this whole arc will be about Mai confronting her trauma from her past relationship and getting her to be more honest with Chungyeon and vice-versa.

I feel like keeping repeating myself but Chungyeon isn't easy to manipulate (read chapter 54 again). Chungyeon doesn't and won't see the manager more than a co-worker/friend.

You can write a million excuses for Chungyeon and blame it all on Mai. And she doesn't have any self-doubt at all, and that's not the point. In any case, something bad will happen at the end of the season and there is no point in denying it. Either Chungyeon will get drunk again and cheat on Mai, or there will be some kind of misunderstanding situation that will make Mai think that she is cheating on her.

I never blamed Mao but whatever

Ok, let's not argue.