I can't help but feel somewhat bad for Kim, even though he certainly hasn't been the best person in these last few episodes.
He approached Chay for his own gain, even after knowing that Chay looked up to (and crushed on) him, even going so far as to ask the boy to write him a love song.
Sure, it's obvious that he started to form feelings for Chay, but even so, he decided to just up and abandon Chay and no longer respond to any of his calls or texts.
But then this brave and shy boy shows up in his studio one afternoon, gives him a handmade gift and confesses to him. The right thing for Kim to do would have been to (gently) turn him down, and then continue to distance himself from Chay completely.
But, presumably overcome with the emotions Kim probably never feels, does the opposite.
And then Chay confesses to Kim once more. This time, however, Kim tries to do the right thing (in the wrong way, of course, but what else can we expect).
Kim was about to leave Chay for the boy's own good.
Only for his plans to be thwarted by the poor boy about to be kidnapped. So Kim hops into action and tries to save the boy but is outnumbered and overpowered.
Chay gets kidnapped anyways.
So Kim does something he never does, he calls his older brother for help. Kim gets involved in his families affairs, all for this boy who had the courage to ask him to be his guitar tutor, who had the courage to confess to him.
He shows up, guns blazing, to rescue Chay (and Porsche, the very guy he was originally suspicious of and started all this for, but that's besides the point).
And now we don't know for this for sure, at least not yet, we aren't sure if Chay was conscious enough to remember that it was Kim who saved him, or if he simply thinks his brother did.
Kim was going to leave Chay for Chay's own good, Kim was going to save the boy the heartbreak of finding out about Kim's identity, about the reason Kim approached him in the first place. Only for that plan to blow up in his face when he has to save Chay, and therefore reveal his identity anyways.
We know this isn't the end of their story, but how will it go from here? Will Kim show up to see Chay, simply to check on him? Will he apologize to Chay, and therefore reveal everything (If Chay hasn't figured it all out by now, that is)? Will Kim try to pull the disappearing trick once more? Or will he decide that he wants to work for the boys forgiveness?