Yep even korean readers who read the novel are also a bit confused. The main point is their real soul and world is in Silence, and the present normal world is just uke's fantasy of happiness, and they both time travel again to their original world (Silence) all the shits in Silence novel plot is horrible thing seme do to him, and they both time travel again before the worst scenarios happen
Basically this manhwa use regression trope. They both died in Silence, but somehow their soul living again in normal non omegaerse world which is just uke's illusion, the uke doesn't even remember his childhood when he's in non omegaverse world, basically schizoid world of uke lol. Their real live is in Silece. They both regress again to their original omegaverse world but uke regress first during the auction and seme regress in chapter 25.
Seme in uke's world remember everything (his sins, his wrongdoings and abused to uke), meanwhile the uke doesn't remember his past soul life. And uke's illusion based on his paintings (in Silence), and seme realized that the scenarios of uke's illusion world almost end when they graduate college, so he thought that he would lose everything once it reached the end, but well they went back again to their real world; Silence, but regress.
My brain stopped working but to sum up what I understand is that theey both died and first woke up in the normal fantasy world that uke came up with and seme just randomly find consciousness there. In that world exist the novel "Silence" which tells the story of their previous life in the omegaverse world from the uke pov. And now they both regressed into their original omegaverse world (?)
Spoilers!
1. Their real world is Silence
2. The "present" is just uke's illusion of happiness, but somehow the seme got into uke's world of illusion
3. Dont take fictional too seriously with logic, basically seme and uke died, seme's soul got into uke's illusions of "happiness" where there's no omegaverse trait (due to uke's trauma), seme is the one reading Silence in uke's world, and he's also the one who sent the book to uke
4. Seme in uke's world basically suffering from loneliness bc he's literally feels like he's in truman show, the world only lit up when the main character is there, the uke. And when the uke left, people literally behaving like a soulless puppet
5. Seme make a wish to go back again to his real world so he could pay for his sins.
6. They go back again but, uke go back to Silence world first, and the seme go back after their first sex as in latest chapter.
7. The uke will soon know his real world is Silence, so yeah all the people near uke in "normal non omegaverse" world is just his illusion
8. Uke's illusion is from his own painting and drawings, the uke (who was in silence before he died) wish that he could live in a world where there's no discrimination with alpha Omega kind of thing, and his most happiest moment is the time he was being good friends with the seme. After uke died, the illusion become "reality" and the died seme who live in uke illusion knows that this is uke's illusion (he knows it because he read the silence novel to understand uke's pov that he never knew when he's alive) and all of the people resembling uke's drawings. Because of this, no matter how many times seme want to confess, it's as if there's a invisible power stopping him to do so, hence seme determined to go back to their real world again. When he go back, somehow he go back at the time before he died.