
During volume 10, I think. As Mikasa said, they're not a typical couple, but the fact that after the talk in which Senpai told him that he wanted Morinaga to stay with him, that he initiated sex, that he is turned on by Morinaga's body, that he's told Morinaga he accepts him (even though what he doesn't accept is Morinaga's horniness), that he praises Morinaga when he's not around, that he listened to Morinaga's request of not living with someone else, and that he explicitly gave Morinaga a home to return to... I'd say they're pretty much established.

so u would consider it more official if senpai said I love u right?
I thought that too cause that was the typical ending/ hype of a romantic yaoi. god ive been reading this for how many years? maybe that's why I think of them as a more official couple even without the niceties cause I realized that relationships vary from person to person in the way they behave with each other and not only that but the way they behave with the next love they find

no what i mean is the affirmation of being exclusive to one another for example if in case there's a blind date going to happen, senpai could just go (cuz his so weird sometimes it might happen hahah) he can, because they didn't really stated that they are going out, so why would i be worried to hang out with someone other then you, something like that hahaha
I know that it makes me a bad person but Morinaga has been so pathetic chasing senpai this whole time that it would actually make me feel a bit better if this new guy could tempt him even a little. Of course not cheating (though TBH even if he did get with the guy its not cheating Morinaga and senpai aren't even dating... at least not to senpai anyway) but if the thought could cross his mind about moving on, he would seem less one sidely crepper obsessed to me.
But I really don't see that happening because Morinaga is a lost cause, plus idk I feel this is not a "date me" situation but something else entirely.