I definetly agree with you. Hui Seong's story felt less like a proper plotline and more like the writers wanting to include a forced message about different and unconventional relationships, but it just felt off. I don't get what they even want me to think? "Open relationships are fine and harmless?" but they showed everything that can go wrong: a child with an unknown father, friends misunderstanding, jealousy from the other girl... it was really confusing.
And I had the same thoughts about the ending. I didn't understand why she had to break up with him for a second time. when she found out he was lying to her and got mad, that made sense. But after a tough time where he was as present and loving as a real husband would be, she decides "Yeah no I don't want to be happy"? The forced breakup trope needs to die and never be brought back.
My stupid ass thought the older brother was Kiho and was shipping him so hard with the Mokha, so when it was revealed that the younger brother was Kiho, I had to take a break from the drama to recover from my accidental second lead syndrome :')
And I had the same thoughts about the ending. I didn't understand why she had to break up with him for a second time. when she found out he was lying to her and got mad, that made sense. But after a tough time where he was as present and loving as a real husband would be, she decides "Yeah no I don't want to be happy"? The forced breakup trope needs to die and never be brought back.