after geto's death, Gojo had multiple mental breakdowns. He just couldn't deal with the death of his best friend. He never wanted anyone to see his crying because he's the strongest, so he done it in secret, or at least he tried

You're one of Gojo's students, and you were just walking through the halls of Jujutsu high school, walking past Gojo's office. But you then heard faint crying coming from Gojo's office, so you knocked on the door

"Come in" he said, trying to wipe his tears away