What the heck was that?

EP 1 and they already made out in an alleyway?????? when they LITERALLY don't know each other?????? and they don't give us ANY explanation as to why JJ followed Sun Oh.

Not just that but before the kiss, he knows that his childhood BFF fancies JJ. So why? how did Sun Oh fall for JJ when they only stole glances a couple of fucking times. Did Sun Oh just one night decided to be a dick and steal JJ from Hye Yeong? What the hell is this storyline. I thought it was going to get better and get explanations later in the next few eps but noooooo it just gets worse. JJ suddenly turns cold and breaks up with Sun Oh to protect him and all that crap when REALLY she was just being inconsiderate of his feelings. Things could've been solved way easier and faster if they had just sat down and talked it out. This drama is far from being realistic.