A major reason the writing in this drama fumbled is that it fails to truly hold Mido accountable for her cheating, and uses her suffering as a shield against accountability. For instance, you have the mudflat fight scene in episode 8, where she basically lashes out at Namgung in order to get him to do the same. Her words that he should have said that they'd try together ring empty when you consider that when he did try in the earlier episodes, she never appreciated that effort, instead she was the one who'd always wanted to back out first because of her failing career and feeling like burden.

• Even after the mudflat fight, even after saying all that about how he should have 'tried', she's the one who once again brings up the one month proposal, adamant on them 'meeting' different people and never backing down on that suggestion— see the contradiction between her words and actions?

• And then we get that monologue from her about how "if the hurt is from you, i'll gladly accept it", and the narrative tries to frame it in a way that makes her seem like some sort of martyr. But when you remove that and look at it from an objective view, her actions just ring as more self-serving than selfless (as many of her defenders like to claim), because she was doing it with the justification to 'get even' and be hurt the way she hurt him.. except she once again focused only on her guilt, instead of the hurt she inflicted on Namgung. And forced him into an agreement he didn't want— yes, forced, because the power dynamic between the two had never really been equal. She knew that he wouldn't refuse, just the way their family expected him to keep being there for her — because his literal life was indebted to them.

• Not to mention, Namgung almost died the day before they had this fight- something Sua points out- and it was as much a reminder of a traumatic incident for him, as it was for her. Yet that doesn't stop her from hurting him once again.

The only reason so many people empathise with her (despite her messed up actions) while simultaneously villainizing Namgung is simply because the narrative continually explains her POV and her intentions (that she loves Namgung so much; but just because you love someone does not mean you're not capable of hurting them), but doesn't do the same for Namgung's thoughts. This is why people seem to think of his development in the last episode as abrupt. If you look closely though, the hints to his final decision are all out in the open. The show begins to lay them out right from the beginning of the second half- from the cheating up until the moment where the older brother blames him for their father's death, and then the conversation he shares with the mother. He says it himself, that he feels too sorry to continue this anymore- making it clear that that was the limit of his endurance. for both the guilt and the unspoken burden of survival he has carried for so long.

The writing trusts its viewers too much (and is also lacking when it comes to later developments of both the second leads), and that's where it falls apart a lot of the times, because it leaves things ambiguous. It's both a strength and a flaw of the writing, but could have been so much better if executed well. Regardless, I loved the ending in that it finally allows Namgung to live a freer, healthier life, and experience a kind of happiness that isn't tainted by the shadow of guilt that had haunted him all those years.