Why does he keep searching her?

I’m being ridiculous because I’m a grown up, but why do I keep finding her in his searches on fb randomly? She was blocked on IG and now she’s unblocked.. and WHEN I confronted him on it, he LOST it and hasn’t talked to me since and we live together.... like I don’t wanna confirm my worst fear but like wtf!!! Is he being nosy or cheating on me? And FYI this was a old teacher of ours who was a student teacher and OBSESSED with him and would always message him. Wtf help :(