ok:
1) this is one of the many reasons secrets are NOT good to have. had he told her since the beginning things would have been different but now he CAN NOT tell her EVER! unless...hmmm no...even if sungah found out about it by herself it would still strain their relationship to some extent...point is if you have a secret you should better let it out as fast as possible before things get to the point where even trying to tell it is going to suffocate you.
2) i still have my doubts about class rep. he just gives this really fucked up vibe off, like he´s some sort of psyco or something you know? every time they do a close up to his face i get shivers...i really hope he isnt some crazy creepster but his face makes me doubt a lot...
3) sungah saying she wouldnt like it i bet it doesnt actually mean shed be disgusted by it but that since she already has a guy she likes she wouldnt want her relationship with joonwoo to break, not that they are that close either but sadly since class rep interrupted her she didnt have time to explain it and now joonwoo thinks sungah is actually a bad person or something lik that.