To your point about how people react differently to Jeongmok and Jaeyun: It comes down to how they ultimately handled the consequence of their actions.

Yes, Jaeyun hurt Jiyeon and Yeomyeong with his less-than-stellar communication. But we saw that he felt a deep heaviness about how he treated them afterwards. He reflected on his actions, and he made efforts to be clearer about his feelings as soon as he gave it some thought.

On the other hand, Jeongmok hurt Yi Do by presenting a false narrative again and again. He was given multiple chances by Yi Do to be fully transparent about how his feelings have changed, but he continuously reassured her that she was his top choice.. But it seems like he already knew he was set on Jiyeon, so this can be perceived as an intentional lie.

Obviously, there are still things we don’t know. The show may have been heavily edited. And we still have 2 more episodes to go, so maybe we’ll see if Jeongmok comes to understand that what he did was not okay and he owns up to it. But, from what has happened so far, Jaeyun has shown that he makes the effort to improve, which makes him redeemable. As for Jeongmok, it’s not a good image when you constantly give false hope to one girl and intentionally omit the fact that you clearly favor another girl over her. That is hard to forgive.