Aside from the 50's pinup torso, what Jungkook saw in Sana that was dearly missing in Nayeon was a lightness, a certain brightness of being. He saw that his confusion had now almost vanished, but at the same time he felt that all his former freedom had also completely gone. He felt that there was now a judge of his every word and action whose judgment mattered more to him than that of the rest of the world. As he spoke now he was considering what impression his words would make on Sana. He did not purposely say things to please her, but whatever he was saying he judged from her standpoint.
But something has been lost. How do you control your impulse to be immediately satisfied? He didn't want to let go of Nayeon. Oscar Wilde's ironic observation applies here: "When God wants to punish somebody, He gives them what they want."
Sana's face twitched. She frowned and lower her eyes for a moment. She hesitated for an instant whether to speak or not.
'Yes, we can be together,' she then said in her quiet voice with its bright jangling notes. She paused. 'I feel very happy when I'm with you.'
Sana's voice broke. She blushed, pressed her clasped hands on knees, and then, controlling herself with evident effort, lifted her head and began to speak rapidly.
'I knew nothing about your feelings. I did not dare to ask you. Then suddenly Nayeon told me you were travelling with us. I had no idea and could not imagine what state she was in, all I wanted was to see you and be with you,' she said, trembling and breathing quickly.