Looking for an anime

I don't remember very well, but I watched an Anime before around 2017 I think, It was a mystery and investigation anime I think about a woman who has an illicit relationship with her nephew or cousin (I don't remember) >! At the end of the anime, she finds the MC in a library and talks with him one last time before going to the police who are waiting for her outside but we find out in the end that the police who were waiting for her were her accomplices and she just ran away !<