
I disagree, when Nakyum says he must stay in order to help Inhun, she immediately dismiss this possibility, saying Inhun can do it by himself and he doesn't need Nakyum's help. She never said he must come back to live with Inhun, she just thinks the feelings for the scholar were genuine and coming from him acting "genuinely" kindly to Nakyum, unlike the feelings for Seungho. It's up to Nakyum to clarify Inhun is a bad person, calling him a prostitute and basically using him all this time tho.

I disagree. She only brings up the learned sir because she is trying to get nakyum to compare his love of seungho with past experiences of love because she believes he’s not actually in love with him and basically has Stockholm syndrome. She directly tells him in the beginning that he doesn’t need to do this for the teacher so that shows she’s not trying to get him to be hung up on a past love. She also doesn’t know the full story of what he has done to Nakyum with betraying him and all. So I think noons did nothing wrong and definitely wasn’t trying to tell Nakyum to still like Inhun but was just trying to get him to realize that Seungho is really toxic and that a relationship with him would lead nowhere.

My point being that she isn't aware that the relationship with InHun also would be 'toxic'. God I hate this word, looks like everyone is repeating a memo.
Clearly she is not leaving InHun as past experience, she is telling Nakyum that he is in love with InHun --- present. Notice that she trashes out Seungho, rightly so, but since she is totally unaware that InHun is another kind of shit, she is not telling warning Nakyum to also give up his love for InHun.
The whole point of my post is to say that Heena clearly doesn't know of InHun's real character and while she is warning Nakyum of one misfortune while comparing to InHun, that we all know is not someone to be in love with.

See, there is a contradiction here. If it's up for Nakyum alone to clarify that InHun is a bad person, why is not for Nakyum alone to clarify that Seungho is a bad person? Clearly Heena is giving advice to Nakyum. People are looking at this with their very biased opinions on characters. They either put someone as perfect and doing absolutely nothing wrong or they put someone as horrible and doing absolutely nothing right.
On the other hand, if Nakyum is responsible for figuring out by himself about InHun, why this change for Seungho? Why someone telling Nakyum about InHun real intentions is not a good thing but only when it relates to Seungho? I don't get why Nakyum cannot have someone who will protect him from InHun, what by the way is even harder to do since he is already influenced by his memories of him.
It seems most of the people replying to my post didn't really bother to understand it at all. My point is to say that Heena, being totally unaware of InHun's real character, is only warning Nakyum about one of the man. Absolutely not her fault, as I clearly, explicitly explain. She is also under the impression of their first interactions, the idea that InHun was looking after Nakyum and apparently she knows nothing of Nakyum being living homeless, drinking and alone instead of being watched and cared for Nakyum.
I wish people bothered to understand the point of a post, understand what is being said instead of taking as personal offense of some kind.
Heena is trying to save Nakyum from one bad guy while convincing him that he is in love with other. Saying that it's 'up to Nakyum to clarify InHun as a bad person' doesn't make much sense if we know Nakyum clearly needs help identifying danger as well, right?
Let's please not be biased towards characters we like and see what the scene shows us. Heena doesn't have a clue about InHun and this makes her (and Nakyum that is influenced by her and InhUn) vulnerable.

I agree. I think the author is very subtle and smart in this scene. She gave us the overview of what the sister thinks of InHun. She doesn't know the true nature of InHun. She doesn't know InHun punished Nakyum to the point of making him ashamed of himself. She asked him to take care of Nakyum and, as far as she knows, he did good by Nakyum so to Heena, Nakyum being in love with InHun is no harm to him.
I hope at some point Heena get to know the truth. It would be great to see her slapping Inhun in the face and knowing those glasses out of his nose for what he did and said to Nakyum. From this whole interaction, I have the impression that the author is setting the stage to have InHun come back and as long as Heena trusts him as 'good' for Nakyum, he will use this as advantage on Nakyum.

That's what I suspect as well. InHun will take advantage of his good image with Heena to keep his influence on Nakyum. It's easy for the sister to know that Seungho is bad but she is totally in the dark that if Nakyum pursues his infatuation with InHun, he will be hurt as well.
I belong to the group of readers who knows the kind of story I'm reading - a classic abuse-to-love Yaoi trope and as such, I know Seungho is meant to be the person who ultimately changes for Nakyum and becomes his protector and this path of the story is also something expected: Nakyum and Seungho are already emotionally involved, they won't be able to stay apart, not for long and this is also the part where the drama changes to outsiders trying to separate them, even with good intentions like the sister or bad intentions like Min, InHun and probably the father when he finds out that his firstborn is taken by a lowborn.
I feel like a lot of people are either too eager to praise or too eager to dislike wha the sister is saying.
Like many of the characters in this story, Heena is not perfect nor completely wrong. She is obviously trying to save Nakyum from a relationship she thinks is doomed so she is not to be hated for that... on the other hand it seems that a lot of people who are cheering her influence are missing the part where she seems totally pushing Nakyum to remain 'faithful' and grateful to InHun. Being under the influence of InHun or keep longing for him is also a misfortune and sad ending for Nakyum because we know the teacher doesn't really care for him and had no problem pimping him out when he needed. She is practically playing a matchmaker here for InHun.
So, I don't know it seems to me we could give credit when it's due but also recognize that the sister may be unwillingly influencing Nakyum to be hung up on a guy who is not at all the wonderful man she thinks he is. The danger of Heena being blind towards Inhun this way is that we don't know yet which way InHun will use to manipulate Nakyum again but having Heena on his side, even if she doesn't know his intentions, may be the real misfortune for Nakyum next.