Let me draw the pattern for you: Jonghyun and Key being the best friends they always start as and having a sleepover (I suppose because - give them a reason to sleep in the same bed...) So Jonghyun catches himself staring at Key's beautiful face while the youger is alseep and he just can't move his eyes away from the beautiful view. It even makes him forget where he is, so drawn in by only looking at Key, he doesn't even realize that his fingers are tracing over Kibum's face.
And yeah - Jonghyun is pretty much in love. Every time when Kibum is close, when he touches him, his heart flutters.
And then there's the open ending where whatever you want to imagine happens. :D