So his first love is the girl up the stairs? And im guessing his first girlfriend is his stalker??? Because he said somthin bout their first loves being connected and in their first life Jaehyun's girlfriend in highschool was the girl up the stairs so if he wants the past to stay the same, he has to stop Hayoung from getting together with Jaehyun so the girl up the stairs can be together with Jaehyun.