
Nami is the worse “best friend” to ever exist, I feel so bad so Sumin right now and for Sunhwa she deserved better.

As much as I understand her reasons not to tell her, I'm sure there had always been chances to breech the subject, Nami's kind of always felt a bit dismissive and even a bit intrusive to me which makes it a bit difficult to like her but I'm trying to figure out of she's just doing things her own way and not clarifying well on her intentions most of the time

Nammi may a sly person and not the most trustworthy of characters but in this case, I don't think she's wrong about withholding the information from Sumin. She's not obligated to talk about someone that didn't even cross her mind until she came along to the reunion party. If Sumin had at least made the efforts of wanting to find out how her best friend was doing sometime in the past, I'm certain Nammi would have told her already. But it's highly suggested she didn't bother trying to make any contacts with Sunhwa after highschool. It's not Nammi's fault that Sumin chooses to neglect her best friend.
I suppose this is another wakeup call for Sumin to get her act together. There's nothing wrong about spending more time with a loved one but she shouldn't forget about other people around her.

I definitely understand why she didn’t tell her at that time but now? she took Sumin to the reunion knowing someone could bring up Sunhwa and Sumin would find out about what happened in the worse way possible, that’s just cruel. On the other hand I find the narrative of Sumin being the only person who didn’t know extremely dumb but I guess it suits the plot.

Let's not put all this on Nami. It's not like she anticipated Sumin was going to bring Sunhwa up at the reunion, considering Sumin herself had never even shown the slightest curiosity about her best friend from school whenever she and her meet up. This gives off the impression Sumin doesn't seem to care about her anymore and thus Nami made the decision that she's better off not knowing anything. And it doesn't seem like anyone else at the reunion would have mentioned her since they already knew she was gone and automatically assumed that Sumin would have learned the news by now since she was meant to be the closest friend to Sunhwa.
I am not surprised at all about Sumin's ignorance of her friend's death. After all, she was the one who decided to burn bridges after graduating from high school, which was clearly evident in Paradise. She was the one that made the choice to neglect other people that mattered to her while devoting her time and affection for only her lover. In hindsight, she has no one but herself to blame for this. So let's not pretend she's completely innocent from any faults committed.

I agree Sumin isn't faultless in this, but I think Nami kind of fails a bit as well in the fact that regardless of wether or not she thinks Sumin couldn't have handled it at the time, it wasn't her call to make, a funeral is pretty much the biggest thing to happen for anyone (It's the last time you could ever see a person / say goodbye), and regardless of the fact that they never kept in touch, Sunhwa's friends did mention being unable to reach Sumin (which means they made an effort to find her) and Nami could have been that bridge. Nami doesn't deserve all the blame, but I think she also made the wrong decision of deciding for Sumin wether or not she should have been able to go. (Nami herself had said she thought Sumin wouldn't have been able to handle it, which begs to ask the question if she really believed Sumin didn't care for Sunhwa) Nami's a little enigmatic for me however, so I kind of want this side story to help us understand her friendship with Sumin and how, despite Sumin's measured distance from keeping close relationships, she remained the constant.

Also hello! It's always a pleasure to see you in the comments section, I always like your well thought out theories (wether or not we agree or disagree about them) the respectful discourse is always nice to see (I kind of wish the fandom mellows a bit though cause it feels like walking into a burning forest sometimes) but I suppose on the upside, it shows just how much the readers have become invested in certain characters which tells of how effective the story telling had been

Nami seem like she did what she thought was best for Sumin, as she was aware of her not being in a good state back then (maybe it was during the time Sungji broke up with her) and figured she would be even more of a mess if she learned her childhood best friend had passed away. It's hard to say if what she did was truly the right or wrong thing. Things aren't always so black and white. Ultimately, I like to think her intentions towards Sumin are good rather than malicious, even if the method she chooses doesn't appear to be the most desirable solution and could possibly make her look like a despicable character. Perhaps it's like the other poster suggested that Nami is trying to prove a point to Sumin, employing a form of "tough love" in order to help her realize and appreciate what she's got.
Anyways, the cat is out of the bag now. Not particularly pleased Sunhwa (an interesting character with potentials) was killed off, so her death could be used as another catalyst for Sumin's character development. I fear this is going to be a rehash of the main story: another redemption plot for Sumin to overcome her emotional baggage, which involves Sungji having to rescue her again from whatever darkness she's in.

That's true, plot wise, I'm afraid of it falling into the same pattern as before. And instead of Sunhwa dying to further develop Sumin, I kind of wish they'd chosen to focus on Sungji instead
(even in the short time we knew her, Sunhwa, to me, feels more developed as a character than Sungji: We know about her parents, her friends, her relationships with them and with Sumin, how she's been friends with her since middleschool, how she falls in love, what she's like as a person and some of her insecurities even)
but for Sungji we don't have much information, What does her parents do / or did before? How is her relationship with them? why does the narrative present it as if she was raised by her brother? (from her short flashback a long way back, to living with him and his wife, Sungji visits her parents in the province once so we know they're still alive)
why does she and her brother have a large age gap? what are her insecurities and wants in life beyond her relationship with Sumin?
I think maybe they could have done something with that, like maybe her brother and wife finally having a baby and what that could mean for Sungji (how that could distinguish his family and her new one with Sumin and what she expects for in the future)
Or even just following the plot point they’ve already laid out with Sumin leaving the company for her professional growth, show how Sungji’s motivations could change in the face of her staying behind and how them being together means growing independently as well.

You're right about Sunhwa. She definitely feels more interesting and developed as a character than Sungji despite her fewer appearances. It's disappointing to know whatever potential she had, has now gone down the drain since the author chosen her to be a sacrifice to help Sumin grow as a person (Geez, how many more drama is this girl going to make?
Sungji is once again looking more likely to play the supporting character: a convenient therapist who helps her partner heal from her past wound. Sadly, I doubt she will get much focus as this last side story seems centered around Sumin and her redemption arc to correct the mistake she made in the past.
yep saying ex is definitely better than saying lawyer, big brain