
To all the people who are unsatisfied with the ending- its a realistic and relatable outcome for the situation. It was pretty clear that Mr Shin was torn between pursuing his relationship with Jaehee and facing the responsibility of a kid with Lora. His relationship with Jaehee was pure and filled with passion because she accepted him for things he was insecure about like his age and fetish. Versus his relationship with Lora which was pretty much just a long history and her one sided envy/regret. Though most people (including myself) would've rathered to see him with Jaehee its more realistic that he took responsibility for getting Lora pregnant.
Even if he did choose to abandon Lora (Which he never would've) His relationship with Jaehee wouldntve lasted long due to the completely different stages of life they were at (Age/carrer/etc)
And at the end of the day it ended up better for the both of them that they split. Mr Shin was able to continue growing his business and get married and start a family. And Jaehee was able to presue her dreams, grown her carrer and finally got together with Sungwoo.
Personally i think she should've ended being single for the reason that is would show her growth and development as a character (But its a romance so makes sense she ends with the best friend)
I feel the same for Sungwoo, throughout one of his main characteristics is his unrequited love for Jaehee and i really wanted for him to move past that. It wasn't until later that i realised that Jaehee was his motivations for everything and that she was his everything. (Personally im not a fan of childhood friends to lovers so i didn't really like that it was his whole personality) I dont mean to sound lie im hating on Sungwoo, legit the opposite he very ;) But im glad his persistance finally paid off in the end

I think one of the reasons so many people is hating this story is that the plot calls for a very mature audience, and that's not only about their age. One truly must understand the different motivations and not so subtle life issues that are represented here.
Still, even though i hate this feeling of unfulfillment, I understand this is very well written, it was realistic, reality is never sugar coated. As you said, the ending was way more sweet that it could have been.
For me, one particular frustration is that the main couple never did manage to be direct and transparent with one another. She never knew the pregnancy came before they fell in love, she never knew how much he loved her. Same with him, he thought she was seeing someone. They both still ended up thinking the other was cheating.
WHEN I TELL YOU I SCREAMING THIS WHOLE CHAPTER OMGGGG I LOVE THIS WOMAN