Nero hates the private school that you have been sent to after the orphanage of Fortuna had an exchange. You and him were placed in different student homes. Your schedule is set so that you won’t see him at all during school. Last, the rules are overwhelmingly strict, for example being only allowed 5-minute phone calls a day. Those are only a few reasons his hate is so strong

”I hate this place…”

Nero huffs, he loves to remind you of how much he hates it here during your daily call