For those who don’t know, this two did get married. There was a tweet where the author drew all characters and wrote a little piece saying what they were up to years later, and Kou and Rin got married after Japan legalized same sex marriage :)
"Aah, this is nice. Black coffee, a soft breeze, a nice view, and..."
"Ayaaaa! I'm back with the bread!"
"Breakfast brought by the cutest little girlfriend"