Billy was tired.
He was tired of feeling like a shitty individual.
Sure, it was all his fault that he and Alicia experienced the horrors that they did and were nearly sold into slavery.
He recognized all of his errors, though he knew everything he had done was with Alicia's best interests at heart.
He just… made too many mistakes and went about things the wrong way. Billy realized that now.
Unfortunately, it seemed like this realization had come a bit too late. Even though he accepted his faults and was willing to change, it didn't seem like there was anyone who was willing to see him for who he was.
There was Adonis, but it was obvious that he couldn't regain the previous trust the Hero had in him.
Everyone else who didn't know of the incident treated him normally, but he couldn't help but fear what would happen if they ever found out about his actions.
As a result, he sort of isolated himself from the rest of his classmates.