Oh wait, that's right. No, I don't wonder because I just read the chapter. He's obviously heading back to get that and caught sight of them because they're kissing in front of a set of windows that anybody could be walking by because they're not exactly on private property or something. It's a friggin' school, teachers and students tend to be wandering around schools for some reason. Like, I'm not going to @ you for this but damn dude your post deserves some snark.
i tend to move too quick in relationships so this is almost giving me good tips on how to reason with your S/O and avoid being manipulative, good stuff
As early as this chapter it's pretty obvious that Yuu is not asexual. I can see why people think Yuu might be aromantic, but I don't know how you read to this point and think Yuu is asexual when she clearly has interest in physical intimacy.