If they cheated...
Jungkook: wouldn't even be able to say it out loud. He'd just wordlessly hug you from behind and start crying or mumble that he was so sorry.
Taehyung: would inappropriately start chuckling nervously and get really fidgety, probably just starting off with a "Jagiya, i may have messed up. Bad."
Jimin: would try not to tell you if it was a one-time thing, but eventually he'd be overwhelmed with guilt and confess, saying something like "I don't deserve you."
Yoongi: would be oddly sweet, even cuddling with you, and only afterwards he'd admit, quietly telling you and saying "I know what i did was wrong, but i don't know what else to say. I guess i'm asking you to forgive me."
Hoseok: would be very emotional. At first he'd try and be really cutesy and flatter you, telling you how great you are and how you're too good for him, but once you ask him what's really going on he'd break down completely.
Namjoon: would be serious and grim, realizing that you could very well leave him. After telling you, he wouldn't ask you to stay, he'd even say that he understands if you don't want to, but his eyes would beg for him, pleading you to give him another chance.
Seokjin: would be straight-forward like Namjoon. However, he wouldn't be able to hide how scared he is. He'd keep repeating over and over again how sorry he is, terrified that you'll leave. "I promise I won't hurt you. Never again."
