First off I had no issues with the ending as id already been hugely disappointed well before that. The open ended nature was an achievement given what came before. This IS NOT a realistic slice of life these are not average or ordinary lives. Also not having a happy ending or a show being full of misery does not automatically make a show more realistic than a happy ending rom com.
This story if you want to call it that is not anything. Two peoples lives intersect and one persons actions the FLs have huge impact on the Mls not so much the othwr way. We see so much more of ML life that we could onclude this story is about a man whose life is dominated mostly negatively by his relationship with an incredibly toxic flawed and selfish woman. This may seem unfair as he is a frustrating chatacter at times but the worst of him is usually reacting to his relationship with her and he always wants to maintain it whereas the worst of her is always about her thinking only of herself.
The interactions with her and the Doctor are what realky majez it impossible to see any hope for this story or relationship. She is with ML fully committed but from the time this guy appears she indulges him until she is in fact cheating even if its not physical though she finalky rejects him just!! As bad as that reflects on her whats worse is we are told explicitly that the break up is not because of him but following and judging length of the time skip she marries him and has his kid almost immediately after breaking up. The fact that no time is given to explain this or explore this in the drama is unfirgivabke abd makes everything else meaningless. Once she has the child thats it game over. BIG SPOILER AHEAD

The fact that the writer resorts to the childs death as the device to return her to Korea and reunite is distasteful to say the least. Anythig that happens after this is just not fate or meant to be its just tragic.

True to form the FL meets ML and of course does enough to sgaje him up i to breakimg up with his fiancee but doesnt want anything else.

If a woman like this is supposed to be offered as slice of life realistic its a big disservice to women.

He is just a man who cant get over his first love keeps meeting her and getting himself ruined tbat is the only consistent part more toxic and abusive than realistic IMO.
Aside from this there is not one really likeable secondarycharacter or story in the whole thing. Its uncanny. The FL brother is a selfish Ahole similar to FL. The FL friend is portrayed as pathetic and at a crucial point without any reason we can see compketely slates ML to FL.

Even the blurb above here is compmetely misleading. It is gratitous angst and cruelty with no resolutuon or meaning dont wate your time im sorry.