Cute and Submissive is all you can think about when you think younger. That's what they all thought as well when they figured out their feeling's for the younger. He was cute and pretty, he was perfect... The idea came to them that maybe they should share with each other. It would be a mess if he only chose one. ...
Jimin was only supposed to be helping Jungkook out seeing as they're "best friends" and what are best friends for if they can't help you out right? Exactly, but you know, in a situation of friends with benefits, feelings are always involved eventually... even after they've clearly established the whole "no homo" thing...