, you miss some point here. aizawa did talk openly to her but doesnt mean he's with her. he's being passive about sihori's sitiation. he just gather the evidence than being the one nitiate it, didnt he also unaware about the video, and the vid isnt the one who's taken by aizawa. It feels like if sihori asked about it way before aizawa might just give the evidence to her and give her a choice to end it with her own hand, about the other boy situation, it can be interpreted by aizawa find his note and tell him what will happend if he killed himself or encourage him. but it doesnt clear yet