Based on the next chapters raws it seems that in the past haeil hurt pado and broke up with him because people were bullying them and spreading nasty rumours about them. Im not sure if haeil thought that pado told someone and thats why he hurt pado and dumped him, or if they were caught kissing at school and haeil lashed out to protect him / he was scared. Either way it seems like haeil is going to do the same thing again next season, but I hope pado doesnt let him try to go so easily again. (Yoon pado haters quiet asf now!! I know yall feel stupid)
Also I was wondering why Haeil and pado never knew they went to the same school before that day at the motel. Haeils memories were fuzzy from his drowning but pado shouldnt have been so shocked to see him!