Disclaimer: FANFICTION
Jungkook was careful not to bring up Yeri when he was with Seulgi. Whenever he brought up Yeri's name Seulgi would color deeply, as she returned his misgiving with some haughtiness. Jungkook did interpret the heightened color in the way most gratifying to himself, and thought he never saw Seulgi look more attractive. Seulgi, whose opinion was forming itself that very moment (as opinions will) under the heat of irritation, thought Jungkook was uncaring in that respect.
Jungkook was not blind to the dangers of such friction, but he had plenty of confidence in his resolution to avoid it as far as possible: being in his mid-twenties, he felt himself experienced, and he felt he loved her. Yet the difference her presence made to him was not always a happy one: he felt that she often inwardly objected him.