
From my understanding (I might be wrong) in the real world they were in a mall with mc, ml, and sister until the mall collapsed, while they collapsed rubble damaged the MC and ML but the only one who was badly hurt was the MC that's why he's always sick, so yes they are in the sisters novel. I believe the brother is either the sister or someone else but they had memories as well but forgot them or smth among those lines thats why he's acting weird. This is a big plot twist so bewrare : from what I can remember once the wake up the rubble falls on them killing the ML while he was saving the MC. more happens but I lowk forgot sorry ╮( ̄▽ ̄)╭

Beriio has most of it right. A lot of people in the novel are from the real world. The ML was in love with MC but things happen and their relationship goes bad. They meet again in university and ML is still in love with MC but angry about the past. MC agress to go on a date with ML to try to clear things up. They go to the mall. MC sister and her friend and some other people who are friends with MC are there. The roof collaspes, all but MC die. ML protected him so he lived but in still crushed and dying. Time passes different in book world, so whild MC sees ML die he is suffering in the dark, looking at the face of the person he loves who died trying to save him. That's why he's sick, he's not dead he just suffering in pain and because of the time difference he is suffering and dying alone in the dark for years. When he remembers everything he is resentful of ML for trying to save him because if he hadn't done that the MC would have just fully be in the world of the novel.
This novel gets super dark. Not just the obsessive ML in the novel, but what happened in the real world too. When it was revealed why the MC is not well, though that's not something in the novel, it was genuinely upsetting. I couldn't stop thinking about it, I talked to people about it because I had to share since it was really bothering me so much. It's just about the worse thing I've ever read in a novel. I'm sure that some people won't agree with how bad it is to me. But it legit caused me to have an existential crisis.