School friends you say, welll... I haven't got anybody who'd be good at that actually but I mean, Pietro exists and occasionally tolerates persistent people??? He secretly wants to have friends, but doesn't want to show it and also assumes no one will like him anyway, so he acts like an asshole 99% of the time. But like. Maybe he took pity and helped Jack not flunk a test once and now the pact is sealed? Or something.

ETA: On second thought, the above could be fun to actually thread out, if you just want to handwave they share a class (French, Civics, European History maybe?) and Pietro has previously been a dick.