Why would you follow a girl on instagram that posts nude photos (but like not completely , but enough) and you’re in a relationship?

She posts like her naked behind and she poses sexually. It’s definitely not a friendly account and she doesn’t follow him back and he just knows her from school, they aren't or weren’t friends. I hate that I snoop. I hate that I’m so jealous. But it seems wrong, like he could be looking at those while masturbating (even though he said he stopped porn, maybe this is his way to be sneaky.) Idk