Ienai Himitsu no Aishikata

Highschool teacher Nao Saeki is secretly a hardcore otaku who loves yuri manga. One day, at a doujinshi convention they participate in, Nao is eager to convey her feelings to "Nyapoleon", an artist she worships. However, it turned out to be a girl from her school, Haruka Kurumizawa, and moreover, she had to help her. After the event, they decided to go out for a meal, at Haruka's suggestion... When she wakes up in the morning, there is Haruka in the bed...?!

(Source: MangaDex)