Dowan knows that chamin has sexomnia. In one of the early chapters they are in a class where the professor is explaining sexomnia and dowan says something along the lines of "I never would have thought that sexomnia was real until I saw it up close" *glances at chamin*
Hmmm I took that as him speaking from the future...
That is from the future the recent chalter are the flashbacks befire he knew about sexomania
Yes but he doesn't know that, YET. Chapter 1+2 are set in the future where he does know about it, while chapter 3 onwards is set in the present where he doesn't.
If it were chronological, why would Dowan act like he knows and wants to put a stop to it in chapter one only to be surprised by Chamin's behaviour the first time he approaches him at night chapters later? It's because that first chapter is a scene from the future, to let us readers know what the situation is since our main protagonists are not going to be privy to the details for many chapters to come, aka dowan doesn't know.
I'm not sure why after every chapter there's a horde of people confused about whether Dowan knows that Chamin's essentially sleep-walking or not. He doesn't! I mean, it's kind of the point of the whole story? Isn't it a bit dull to read if you're not clenching your fists in worry/anxiety/tension every time a clue comes up (like Chamin being oddly well-rested because he's actually been asleep the whole time!!)?
I mean, no disrespect if you didn't get it for some reason, but the ones who are angry at the story and author, that's just not fair. It's been very clear in my opinion.