Sa-young died and the world was ending so J used the watch to turn back time.
Which created the 2nd timeline.
The chicken owner created a space for J using his memories as a sort of haven that helped him to keep going (endure), which was the room with Sa-young.
The talk about being the axis when turning back time should get more explained with time so I don't want to spoil what it means just yet

Can someone please kindly explain to me what happened in chapter 72 and 73? I’m really really confused right now, maybe I am just sleepy but idk what happened fr. Please, kindly explain to me. TnT