If you reread the story again and go around chapter 170 or so, there is a part where jiwoo gets jealous because the Patrick kid likes jiyoung. Then jiyoungs bro (forgot his name) says "nah you can't be with my sis cause jiwoo is with her already". Then jiyoung says to jiwoo "looks like we are together". I remember people saying nah it's weird but it makes total sense.
In chapter 172, jiwoo and jiyoug apparently started dating. Around the ending of that chapter, she States that because now that their dating she won't be accepting anyone else's dating requests.