So kdj as the book lover (and fan of the traumatized protagonist) decided to actually interact with dreamer yjh and comfort him. Which as all trauma bois go yjh got attached. A bit too attached over time. He tried to meet kdj as often. And since kdj's a dream walker...

Forcibly induced sleep on himself. And eventually kdj realized and was like "Hyukie don't do it... you'll find me eventually." And kdj slowly stopped regularly being in yjh's dreams and then yjh got insomnia. He didn't want to dream and it not be with kdj after all.