Houkago no Shokuinshitsu

Basically a romance between two high school teachers - Kawase Mitsuro and Kazama Toshiaki. Complicated by Mitsuro's hesitation to accept Toshiaki's very open declaration of love. Slightly complicated by a bit of jealousy on the part of Mitsuro's younger brother Hitoshi.
Note: in 2005 the story was re-released in two volumes under titles: "Hatsu Natsu Monogatari" and "Koutei ni Ouka Ranman" by Daitosha with newly drawn covers.