The real world is the ABO world. Their first life is what Heemin considers the "novel" world, but since everything was traumatic for him he creates the non-ABO world to cope. Hun somehow ends up there with all his memories and tries to be a better person to Heemin who doesn't remember their first lifetime/real world. Then they end up back in the real/ABO world, but back in time to when things first started going bad between Heemin and Hun. Heemin thinks the non-ABO world is the real world and the real world is the "novel world". Hun eventually remembers everything, both their first life in the real world and in Heemin's non-ABO world but doesn't want Heemin to remember their first life. They're both trying to make the current timeline/life better. Hence why things are different and certain plot points are either coming up sooner/being resolved quicker.
The real world is the ABO world.
Their first life is what Heemin considers the "novel" world, but since everything was traumatic for him he creates the non-ABO world to cope. Hun somehow ends up there with all his memories and tries to be a better person to Heemin who doesn't remember their first lifetime/real world. Then they end up back in the real/ABO world, but back in time to when things first started going bad between Heemin and Hun. Heemin thinks the non-ABO world is the real world and the real world is the "novel world". Hun eventually remembers everything, both their first life in the real world and in Heemin's non-ABO world but doesn't want Heemin to remember their first life. They're both trying to make the current timeline/life better. Hence why things are different and certain plot points are either coming up sooner/being resolved quicker.