what "feeling" is Finny sorry about having in chapter 5 ?

Finny is sorry about having the feeling that Gene might have done something wrong on the tree that day.

Then he glanced back at me, Tm sorry about that feeling I had.” I couldn’t say anything to this sincere, drugged apology for having suspected the truth. He was never going to accuse me. It was only a feeling he had, and at this moment he must have been formulating a new commandment in his personal decalogue. Never accuse a friend of a crime if you only have a feeling he did it.