It's a collection of one shots and in the first story two people use the smoking room just so they can see each other. One of them even got into the habit of smoking just so they could keep seeing the other person.
http://www.mangago.me/read-manga/datte_oishii_no_ga_warui/
It's the first chapter of this one!
I love both the couples too much. Even though its sad now I hope at the end of season 4 both the couples work out their shit and are happy. A tragedy would just hurt so much noooo