Gene certainly learns from his experiences and matures in the book. He faces his darker side in many ways. The first frightening thing for him to face is his jealousy towards Finny due to his lack of self-esteem. He is not unlike many adolescents who discover their true character after having done something shockingly horrific. Gene discovers just how jealous he had been towards his best friend when he jolts the branch of the tree limb they're on and his best friend receives a shattered leg as a result. He avoids confronting himself about his issues, but eventually does, and eventually confesses to Finny before school starts up again in the fall. Surprisingly, Finny won't accept his friend's confession and played it off as if it didn't happen. Finny doesn't accept the reality of Gene's mistake until right near the end. Yet, during that same year of school, Gene also faces bullies, helps others like Leper, and learns what it means to be a loyal friend. Psychologically, he seems to be the only one who is able to pull himself out of his delusional state and to face reality. Where once he thought Finny was "out to get him" he later was able to figure out the truth. That's more than Leper could do, for example.