
Wait in what chapter did Lloyd tell Javier about the soul transmigration thingy??

I don't think it was ever said directly. Javier figured it out and even talked with the younger brother about it since he was so obviously not the Lloyd they knew. He knew Lloyd could hear but talked about it anyways. They just know that the other knows and don't directly acknowledge it, at least until now.
The closest thing there was to that was when Lloyd was about to die in one of those ending previews from that sickness caused my the weather and overpopulation. He knew he was about to die, so he was going to tell Javier everything. Javier knew this and didn't let him say it like if he did it would make the fact that he was going to die a reality and that it showed that Lloyd had already given up on surviving. He didn't want to accept that Lloyd was going to die.
So yeah, it's mainly been shown in their behaviors that Javier knows and Lloyd knows that he knows.

Someone please give me spoilers, the drama is too much for my poor heart to handle

Spoiler of the whole plot!!! (As I remember them and my memory is a disaster so be warned)
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(I read this a long time ago so some details might me wrong but goes something like this)
His "friend" put him in the novel, he and his sister have that power. I don't really remember why he did it though, the thing is Hyeonjin starts working for Mujin, drama ensues and for some reason that I don't remember the MC dies, I believe his friend told him it was so he helps Hyeonjin? Anyways, he dies in the novel because his character was supposed to die anyways and returns to his original world, there with the help of his friend sister is able to return to the novel but as himself (since Yeonwoo is dead). In the meantime hyeonjin and mujin become friends because they both lost the MC and are grieving, and get together to drink. MC and Hyeonjin meet and I believe he ends up recognizing him or something like that and they end up happy ever after but with MC in his original body.
They are one of the cutest and perfect couple