I'm not upset, because I prefer this manga to not abruptly end here. For those saying it was a cop out, it would have been more of a cop out to have Ayumu throw away his pride which was the main point of the manga for an easy win without much reason other than her letting him have a freebie. At least we got to see senpai's blushing confession-expecting face.
Also, I've seen the art at the end but I didn't know she was saying oyasumi. Assuming she is initiating a lap pillow, and this I am okay with.