Overall, I liked the drama very much.

In terms of the 2nd lead couple, I thought that they should have paint more attention to the revelation that YJ was seeing DK behind HS's back for more than a year prior to running away with him, because that's pretty much a game changer. I would have had no problem with her deciding that she didn't love HS anymore and wanted to pursue something with DK, but then the least he deserved as a human being, and even more as someone that by her own admission had stayed by her side for almost a decade without even so much as getting coffee with another girl, was to be treated with a minimum of respect and honesty.

Frankly, I have seen some rather delusional takes, such as one person painting the picture of a promiscuous artistic environment, and a famous public facing artist, as opposed to her "hermit" reclusive boyfriend, attracting attention and wanting to "upgrade" the boyfriend with respect to the "old" throwaway model she had been with for so long, thus going for the rich fop instead. Now, there are plenty of tv shows where young people that have always been together decide to break up, though this "upscaling" seems utterly superficial (and she was around 27/28, not that being young means being superficial, in terms of inexperience/immaturity... in any case, they don't have anything to do with loyalty and honesty, the golden rule of treating others like you want to be treated, which is pretty universal and requires no particular wishdom of the years). But the show, while not giving precise details on what happened, clearly:
1. Does not make the artist environment out to be particularly filled with flaky, superficial, disloyal or even promiscuous people (plus this is SK there is high expectation fo public figures)
2. Does not at any point imply that she was relying on a man or going for someone more rich and successful, and the very notion is very disrespectful.
3. Makes it plain that HS also had girls going after him, he simply didn't want to partake. He was no hermit (if anything, one could say he saw more people on a daily basis that your solo painter) and *worked* in the city, the house is merely a villa on the hill, which many rich and successfull people have without being socially isolated -he has a car-.
4. Makes it plain that when she met DK she was no famous star, having just had her first lackluster exhibition.
5. She clearly states that she was in love with DK at the time, this was not her going for someone else because she was wondering what else was out there.
6. In any case, I don't think one can make generalizations about artists in the first place, particularly in a different culture like SK with certain expectations for behaviour, and we are not exactly talking about the typical male rockstar sleeping with their groupies, at least that's not how that environment was depicted in the show. It was classy and aloof. By the same token she didn't go partying hard or do drugs. And even if she was in a community where disloyalty and dishonesty were prevalent, it would say something about their behaviour, not on the morality of hurting, humiliating, deceiving one's partner, a behavior that is universally considered objectionable to say the least (again, this is separate from things like poly, etc., it's about honesty, not where to set the boundaries and whether sex or even romance with multiple people is in or out, the specific rules have to be negotiated with one's partner anyway). To be clear, if you are in an environment where theft and street violence are more common, it does not make engaging in such behavior moral.

Another insane take was the idea that having a more than year long affair and running off with her lover somehow being described behaving more like men to make her way in a (man's) world, I find the take to be an utterly insane generalization: while men are less faithful in general, not being faithful is not a defining characteristic of men, and in particular prior to her betrayal it was most definitely not a characteristic of HS, and certainly didn't help her nor anyone else make their way in the world (unless one is insinuating something like that DK only sponsored her because she slept with him, which seems insulting and the exact opposite of female empowerment). Much more respectful to say that she made her way in the world through her own talent. The only way she overturned gender roles there was proposing, which was cool, for the rest, her femininity has no impact on choosing her sexual partner (FL did it while passing as a male) or her career (surely it's insulting, not empowering, to think that she didn't get where she was through talent, or imply that DK only helped her because they were together).

Now, to tackle HS's behaviour, looking at what actually happened, they are the same thing in the same way that a paper boat and Bezos' yacht are both boats (I guess that technically they both float, but comparing them is like comparing a candle light to the Sun). HS had a small unreciprocated kiss with a girl that was not interested in him anymore. Frankly, in her place, I would be too ashamed by the sheer hypocrisy of the word about to escape my mouth to even mention words like not being able to trust, feeling pathetic, or pride, let alone mention reading a message when he was alone compared to more of a year of lying to his face in the same phrase.

Frankly, there is a long, long way to go before they can be considered to be "even". Even if he had cheated on her with another woman he fell in love with for more than a year, and then run off with her for another two without a second word, only to reappear all of a sudden two years later, expecting to find her there and ready to take him back, he still wouldn't have gotten even, because she would have done all of the above to someone that had always loved only her, after almost a decade together, and that had never even drunk a coffe with another girl, rejecting any other possible partner, on top of putting up with more than a year of her lying to his face and meeting DK in secret, and then running off for two despite his begging, only to return and dare to demand he takes her back now that she and DK have broken up... followed by a complete lack of care for his point of view or any desire or attempt to rebuild trust (if it was even possible), while he would have done all that to the very same woman that did the aforementioned cheating and running off and coming back after two years without hearing a word having the gall to ask him to take him back, without doing anything to regain his trust. Not that if she had tried for real to get his trust back it would have made any difference to what she had done to him and her complete lack of a leg to stand on and complain, in any case, just pointing out the kind of person that he would have been cheating on. In terms of karma and poetic justice, him or DK doing such a thing to her would have been something that she wouldn't have had any leg to stand on and complain about.

When she tried to threaten to leave with DK, the man she had cheated with for more than a year and run away with for two, until she showed up uninvited again, telling him that he still loved her, it should have made him more convinced to just break things off with her himself and go look for someone else. She has the gall to threaten to leave him for the guy that she had cheated with, and he is supposed to beg her to stay (which he unfortunately does)? Telling her to not let the door hit her on the a*s on the way out should have been the more appropriate response. The question is really not how he could have fallen for someone else after the hell she put him through (i.e. all it took before they could finally be together, specifically him with her... here she is probably forgetting that she was the one that went back to him after breaking up with DK, but certainly HS groveling and begging her to stay made it easy to forget that, and in any case it was basically a matter of showing up and asking, she didn't even attempt to do anything to regain his trust -doubtful whether it would have been possible in reality, but here it was all swept under the rug-), but rather how could he not have fallen for literally anyone else, or even chosen to stay single. And the hell was not finished even after getting back together, what with him being taken for granted, or the fact that the psychological and emotional trauma and suffering he went through and his understandable insecurities are ignored when not mocked, and he doesn't feel free to talk for example about how he feels regarding DK, and is mocked when he does, which he then goes along with and plays it cool, while being unable to open up and having his insecurities taken seriously, if they are not outright ignored or farcically twisted around like the pain he conveyed at being lied to for more than a year before she run off with her lover, which was completely ignored by YJ prompting the absurd question of how he could love someone else mentioned above (answer: how could he *not* love someone, anyone else, after being put through that and having her react in such a manner to his confession of utter pain? Only by not loving himself or having any self respect and self dignity left).

Talk about two weights and two measures, boundaries extremely loose for her, stricter standards for him, he has to guarantee that he will not feel anything for anyone else ever. Not talking about actions, but about straight up thought crime, like Orwell's 1984... Newflash, nobody can guarantee that, as we are in control of our actions, not of our feelings. We have thoughts and emotions, and then we have actions. The latter we control, and through reason we can orient our thoughts and judgment and evaluate our course of action: for example, if we are in an abusive relationship, we can choose to leave despite feeling attachment due to feeling from a happier past, and even come to the realization taht the person we might think we love and were convinced would have never hurt us in such a manner might exist only inside our head, and the real one does not deserve us. But you cannot choose to love someone on command. Emotions (which you feel, but are not tools of cognition), and spurious thoughts which come into your head whether you want them or not (and you can observe when you meditate, and let go), vs reasoning, vs actions. The reason the law punishes actions and not emotions and thoughts is that actions have the peculiarity, over those other two, that you can control them. You cannot choose to believe something you don't really believe simply because you want to (well, maybe there is brainwashing), and you cannot force yourself to love someone you don't. We can and should decide whether the love or attraction we feel for someone means we should pursue a relationship or not -maybe they are abusive, or they are in a relationship-. But we cannot force ourselves to, say, love someone on command, the only guarantee is to be honest and upfront with your partner and identify what the boundaries are and whether you want to carry on the relationship or pursue something with someone else.

In that respect I was repulsed and didn't agree with in the least with her minimization of ML's feelings for her when she said that he didn't love her because otherwise he would have tried to steal her from his cousin: there are other boundaries, and decent people don't try to get between two people in a relatioship, and hurt people that never did anything wrong to them -because they don't know them-, or that they care about -in this case, family-. This mentality is frankly completely self centered and self serving, and toxic, and reveals some rather ugly truths of her psychology regarding boundaries not to cross, etc. Note that when HS kissed her, FL was not with HS's cousin at the time -she was just getting infatuated, but obviously he wasn't even sure if she was really into his cousin, in fact until very recently she was into him instead, he missed by a very tight margin-. Plus, his cousin still thought the girl was a man. Otherwise I doubt HS would have considered coming between them, despite the fact that the latter routinely tried to get into his own gf's pants, so it's not as if he would have had any leg to stand on anyway. There is a point there about not trying seriously or for real, in any case walk by the river... had she reciprocated, not sure what would have happened, giving the benefit of the doubt that he would have pulled back, despite being rather inconsiderate in constantly flirting with her... I don't want to think that he shares YJ'S mentality, and wished he would have pushed back and called her out on that at any cost, including lying and deceiving other people who did not deserve it... wondering if she would be singing the same tune if she was on the receiving end for real, by someone that was determined to come between her and her boyfriend, rather than by someone that wasn't interested like FL, which was therefore not a threat-. There is also the concept of competing for the attention of the same person, versus coming between two people in an established relationship and trying to break it apart, which is what ML would have needed to have done in order to try to get YJ to leave HS.

Some quick final thoughts. Coming back to the topic of cheating, I wonder if her lover cheated with some kind of model or not (he does not mention it, she bring out a model when he asks about the musician, her bf... maybe it was just someone DK saw as a rebound after the breakup, while still pining for YJ?). Also, not to look into anyone's linen basked and go into *that* much detail, but no uncertainty about the kid's paternity? She was back for a month if I recall correctly when she slept with HG the first time. Not sure when she broke things off with DK exactly, I guessed close to the time she went back to SK.