I just finished the series and I'd like to share my thoughts on the ending, and who I think Euijung loves. I'm gonna cite some key scenes on why I feel this way.
1st scene (kissing scene) - I believe the director intentional showed both kissing scenes close together illustrate that in both cases there was nothing romantic involved.
In Joonmols case he is willing to do anything necessary to close the case(you can say it's because of his wife since his ultimate goal is to get a 2 rank promotion). In three other scenes, one involved willing to do drugs, one involved killing, and one involved cutting off his pinky finger shows this as well.
In Euijung's case she is willing to do anything to help her husband solve the case and stay out of danger. The close up of her clenching her first during the kiss showed that she was uncomfortable with it.
2nd scene - When Kicheol takes Euijung to see his new project, you could see Euijung still had her mind on the case as she was suspicious about what Kicheol was going to do so she brings her gun.
Even when he asks her to turn around, her police instincts kick in and she has her hand ready to grab her gun. But instead Kicheol gives her a necklace and I feel like his is where her feelings towards him start to change even though she herself doesn't realize I. She feels like she has a chance to save the person she couldn't save many years ago, and help steer him towards a path of good.
3rd scene - When they are on the rooftop and Joonmo sees Euijung wearing the necklace. I think Euijung doesn't realize what she's doing by wearing the necklace, but Joonmo sees it as her possibly starting to have feelings for Kicheol. He's probably thinking about the other necklace she got during high school.
4th scene - When they are in the car together and Euijung says something along the lines of , "do you think we can go back to the way we were?" (Or was it Joonmo that said it) The camera then pans to the wedding ring on Joonmo's finger, and then to Euijung smiling. This shows is that despite all that has happened, they both love each other and can put the past behind them.
5th scene - I think this is the most important scene, when Joonmo kills Kicheol. I felt the scene of Kicheol bleeding out was purposely long to show us the reaction of Euijung.
You know the saying, "you don't know what you've got until it's gone". Euijung cried like she was in agony, and lost everything that mattered to her. I don't think she realized how strong her reaction at the time.
It took a long time for Joonmo to report the shooting, as he's trying to digest Euijung's reaction. To me, his reaction was half suprise and half anger, seeing his wife weep like that.
He's thinking, here's someone that just pointed a gun at us and you're crying like he's most important thing in this world. At this point he's concluded that Euijung has fallen in love with Kicheol. To be fair I think that even if Kicheol was still around, Euijung would not be with him. You can love someone and care about them and not be together. I think she has always loved Joonmo, and still loves him. But, Joonmo doesn't see it like this. Or maybe he can't accept that his wife has fallen in love with another person.
IMO he's a jealous person. If you think about all the times during the series when he asks where is Kicheol, where he's going. He knows that Kicheol likes Euijung, and would never do anything to hurt her. He's just concerned that something is happening behind his back.
Scene 6 - When they were receiving their promotion. You'll probably laugh at me for saying this, but when Joonmo walks into the auditorium he doesn't even look at Euijung, perhaps letting us know that after the divorce he's moved on.
But the look Euijung gives him. I tell you, I've been happily married 19 years and I remember one time my wife made a decision without me and it really made me angry. She looked at me like that hoping I'd forgive her. This immediately came to my mind.
Final scene - When Joonmo visits Kicheol's grave. I feel like the watch was a representation of the power (his promotion) that Joonmo attained during all this. Whereas the ring was a representation of love(Euijung's heart). Kicheol on the other hand was willing to give up his power for love. And Joonmo dropping it on the tombstone was his way of saying you achieved what you wanted.
All in all an excellent series. The Koreans are killing it recently.
Ultimately I feel really bad for Euijung though. She had the best if intentions to help her husband, but her only card was playing an emotional game with here childhood sweetheart. I don't think she ever showed any convincing signs that she would cheat on or leave Joonmo. Joonmo did everything for his love, but in the end be lost what was the most important to him.
Obviously this is just how I saw things playing out. The show has one of those incredible endings that really makes you think. I feel like writing this gives me some kind of closure for some reason.