Responses
I think they didn't do it (Shimizu Yuki is not the kind of person to not give us the smut if there was one). But with what Zaizen said, Kiriya thinks he has to options: go further one time and have an unstable relationship or holding back and staying as friends and with that to always have a place to come back to. But well it broke my heart (again):)
http://www.mangago.zone/read-manga/kachou_fuugetsu/tr/7f8bb1ddc2abef55a8d53694e5365f6a_chapter-4/pg-31/
Things not to do as a friend.... so they do it?