I read the full story and you simply are wrong. The end is just a full side story of how Mr. Yoon and mc got together, that isn’t shown in the beginning. He isn’t a new love interest, it’s the same mc who then later dates his coworker. They simply didn’t actually show the full story of Mr. Yoon and him getting together at the beginning and so the author showed it through the sides stories.
The ending for Mr. Yoon is that he leaves and decide to stay with his wife cause she was kind threatening and at the end, in a poor pity job, the author makes Mr. Yoon pity his wife cause she was obsessed with him since the beginning and had feelings for him forever.
He hugs her when he sees her cry for him and I guess he is destined to stay with a woman that ruined his life bc he pitys her and maybe the author is trying to give their relationship a try, which I totally dislike.
I would have liked for him to stay true to his feelings and meet a new partner who could have given him is real happy ending, whether it be a woman or a man.

Read this again after a long time since it’s getting updated with the colored version and honestly I’m so dissatisfied with Mr. Yoon story. Like, are you seriously gonna leave him live with a woman he doesn’t love for the rest of his life, always unhappy and sacrificing himself? Idk man, I feel like there is the need for a redemption for him as well since he has been suffering all his life ╥﹏╥
Obviously, he can’t be with the mc anymore and he already moved on but I feel like it would have been good to introduce a new man for him to love and change his life forever…maybe in the future the author will decide to do a spin off? I truly hope so…