Off topic but I feel like Iheon transmigrated as well#－.－)

Nah, he is already sus since when he is in the world outside the novel.
I bet my money, the story happend in novel is actually real and then after they died, they reborn to the world where Huimin don't remember anything and don't experience trauma and have loving family.
That's why Huimin grew up to be so bubbly.
But Iheon who was reborn there, slowly regain his memory.
And then somehow, Huimin went back to the past world again.
Meanwhile, Iheon of the past slowly regaining both of his memories the bad ending past and the 2nd world memories too.
That's why he said he want to stay at the current world/timeline, because he have memories of everything to stop bad things from happening, he can be lovers with Huimin, Huimin don't hate him and not remember the hurting memories.
After all, 1st timeline is bad ending with both hurting each other until death.
2nd timeline they are only good friends since Huimin have no memories and in that world, same gender couple is not common.