Docchi ni Shiro, Dotsubo

High school teacher Yukino has a sexless marriage with her husband and leads an unfulfilling life due to her own sexual preferences. Overcome with desire, she uses a meetup app to have a one-night-stand affair, but the one she had an affair with turns out to actually be a student from her school. A forbidden, immoral, teacher-student love triangle sex story.

(Source: Hakusensha, translated)