It's quite interesting how this took longer than Asuka confessing, seeing how this was the established pair of the series. There was and still is no Asuka+Kei couple, yet we still had the confession there a while ago. Mayu+Yuuki, however, has existed almost from the beginning but took this long to become official. I wonder if confessing actually became easier for Asuka due to knowing it wouldn't work. It's quite a popular trope people don't confess because they fear the friendship will also end if it fails. Asuka probably could guess the old childhood friends relationship with Kei wouldn't end because of the confession.