His sexuality is debatable but the author said we may learn about his past relationship/s in future volumes. With that, i don't think Morinaga was his only love interest. I also think he does experience attraction but it's just not as strong bc he seems aspec. And the reason he says he's not gay is due to the traumatic incident that happened to him in the prequel challengers where is professor sexually assaulted him. That's the reason he says that. As we can see, senpai is romantically and sexually attracted to him which at the very least qualifies him as queer. I say queer in this instance instead of gay bc we don't know the gender of his previous partner/interest
Oooh I see thanks for the info, where did you read it tho?
On the author's twitter @tkhina you'll have to scroll down a few months/years so I just use the search feature
Remember that "The End" is always in all the volumes final chapter but def, not an actual "ending" for the story itself, I really can't see this ending soon, the mangaka seems to enjoy writing them.
Also, Sempai is never going to call himself gay, because he is not? At this point I'm sure he is one of those "If is you is Okay" kind of sexuality, because he isn't attracted to men or women anyway.