I enjoyed this drama, despite the fact that nothing really happens. But the last episode sucked. Time skip, saccharine, weird long, drawn-out "misunderstanding" and the weird monologue with them speaking at the same time.
She figures it out in episode 20 around 5:25 when she notices the scar on his back and he lies to her about how he got it. In episode 21, around 6:40 she remembers the person who saved her was wearing the cross he gave her and at the very end when they're sitting on his couch she tells him she knows he lied about it and he explains he didn't want her liking him only because he saved her.
My new theory for the angst which is coming, which I much prefer: JJ's mother doesn't accept YS with JJ, so she…
Based on that one scene in the credits where YS and DL are walking side by side - I am 100% expecting the two of them to partner up at some point to take down Linda and get revenge for JJ's father.