Sakusa was the only one who you accidentally touched like that. Every single time.

Even though the classmate was able to see that you were genuinely sorry, Sakusa couldn't.

He saw you as disgusting. You didn't notice it but all that disgust was building up, and he was trying to control it.

Sakusa hated all the accidental touches from you. You didn't notice any of this, and neither was he planning on telling you, since telling the truth would be extremely uncomfortable for him.