In this world of sleaze, gratuitous fanservice and men obsessed with breasts, such a pure relationship is a refreshing glass of water on a hot summer day.
Nah. If I remember correctly it said in the author notes that it was a special chapter of future events. So technically, the sex is canon. Just, not yet.
Page 6: "I might not have been Wakamatsu-kun's first girlfriend." Wasn't it addressed that he has messed around with other girls in previous chapters? Sometimes if feels like details from earlier in the series has to be ignored just to have a small tinge of drama when things get stale.