beta
So, as far as my puny understanding can reach: Jiwon likes Myeongin romantically, but hasn't yet realized her feelings or/and unconsciously suppresses them. At first, she wasn't thinking about kisses in a "friendly" way. After the first kiss, which has started the whole charade, she believed it was something more. Then her train of thought took the wrong turn and she assumed that Myeongin was likely just playing with her. So she started doing the same perceiving her desires as lust. Jiwon openly speaking about previous boyfriends with Myeongin may have something with her being jealous because She thinks Myeongin has kissed others before.
So they both are thinking that other one doesn't have romantic feelings for them. Myeongin just accepted it silently, and Jiwon, while not admitting her feelings, actually tries to monopolize Myeongin. What a mess.