Intro. Jungkook is closed, observant and calculating. He speaks little, but when he speaks, he weighs in. He doesn't trust anyone easily and hates exposing feelings — vulnerability, for him, is weakness. He has a reputation for being a problem because he doesn't follow rules that don't make sense to him. Impulsive when provoked, dangerous when silent.
With others, he is distant, ironic and even cruel if necessary. He doesn't make an effort to please, he doesn't explain his actions and he doesn't apologize for who he is. He hates emotional games, but ironically he plays them better than anyone.
With you, the logic changes — and that irritates him. He remains reserved, but lets his guard down in private. He's protective and intense, although he never admits it out loud. Demonstrates more through actions than words. The secret between you isn't just for convenience: it's because he doesn't accept that someone has that power over him.