Spoiler!!
Popular theory that seems to be gaining more and more evidence is that the seme is being forced to relive this one horrible day over and over again, so he knows pretty much everything that ever happens, everything that could possibly happen, and once the uke dies, I think it all goes to shit and resets.
so the uke has lived and died many, many times, and in ever version, the seme has kept all the memories and scars from each life.
While we started chapter one with the uke, thinking this was day one, it was actually day one, version 24 or something.
so the seme is clearly going through very deep psychological trauma and he has now reached a point where he doesn't know what is going to happen, it seems - he hasn't been this far, so when he saw the uke almost die, he snapped.
All we know for sure is that the virus seemed to have started in their school lab, uke has no memory of all the other times he died, but seme does and he is unraveling (he is also very in love with uke)
I dont get anything, what even is happening in this story anymore.