Wasn't she low on the popularity polls? That's probably why the mangaka didn't really do much with her.
Even so, yui received like a small omake in the end (even though ironically she should have gotten more as well as satsuki) but it just leaves things up in the air since the mangaka did include every other girl in one way or another.
Personally I was surprised that Manaka ended with Nishino... 0.0
I thought that he would snap out off being the good-boy N would end up as a Playboy or a Sex-offender XD
Nah, the mangaka constantly reinforces Manaka's character so I found it reasonable that he ended up with Nishino. I believe things would have been waaaay different if Aya would've confessed though, it's just a matter of missed chances.
Just finished reading this and wish it had not ended. now that i'm done reading it life feels empty lol.
I still can't believe I managed to finish this... manga.