In "A Separate Peace" what, according to Gene, had Phineas alone escaped, and who, in the end, confronted Phineas with this?

Gene states in the end of the book that everyone, sometime in their life, is confronted with a force, trial or issue that is so large, overwhelming and difficult that it breaks them, and changes them forever.  He says that for most people around him, it was the war, that

"when they began to feel that there was this overwhelmingly hostile thing i the world with them, then the simplicity and unity of their characters broke and they were not the same again."

But, "Phineas alone had escaped this" because of his

"extra vigor, a heightened confidence in himself, a serene capacity for affection which saved him."

Gene, from the beginning of the book, had sensed this and was jealous, because he himself was not like this.  He was not confident, serene, vigorous, or capable of the innocent and true affection that Finny was.  So, Gene says, when nothing else in the world "had broken [Finny's] harmonious and natural unity," Gene stepped in and did the job:  "So at last I had."  Through the breaking of Finny's leg at the tree, Finny was eventually broken.  It set off a series of events that deeply disturbed Finny, eventually leading to his death.  It is Gene that confronts Finny and the fact that he "never was afraid...never hated anyone," and broke that unity of character that he possessed.

Gene states in the end of the book that everyone, sometime in their life, is confronted with a force, trial or issue that is so large, overwhelming and difficult that it breaks them, and changes them forever.  He says that for most people around him, it was the war, that

"when they began to feel that there was this overwhelmingly hostile thing i the world with them, then the simplicity and unity of their characters broke and they were not the same again."

But, "Phineas alone had escaped this" because of his

"extra vigor, a heightened confidence in himself, a serene capacity for affection which saved him."

Gene, from the beginning of the book, had sensed this and was jealous, because he himself was not like this.  He was not confident, serene, vigorous, or capable of the innocent and true affection that Finny was.  So, Gene says, when nothing else in the world "had broken [Finny's] harmonious and natural unity," Gene stepped in and did the job:  "So at last I had."  Through the breaking of Finny's leg at the tree, Finny was eventually broken.  It set off a series of events that deeply disturbed Finny, eventually leading to his death.  It is Gene that confronts Finny and the fact that he "never was afraid...never hated anyone," and broke that unity of character that he possessed.