It's Not Just Adultery.

The suspense manga centers on Sousuke Yamada, who has a loving wife and an elementary student daughter. Sousuke happens to see a video from an "Ura Aka" (secret SNS account) of a woman, who appears to be his wife, having sex with another man. Additionally, the video was taken at her daughter's school. Sousuke tries to find the truth by attending the school's PTA meeting with his wife.

(Source: Anime News Network)