Tatasen: Caramel-sensei no Kimyou na Kagai Jugyou

Haruka Ugawa is the most beautiful teacher at school. Her relationship with her beloved Yuu-kun is going smoothly, except for a big "nighttime problem." It is then that the troubled couple happen to meet Caramel-sensei. Their encounter with her begins to greatly change their fates! This is a story of teachers seriously grappling with their worries about sex!!

(Source: Kodansha, translated)