What did leper tell gene about his escape? Why did he do it

Gene goes to see Leper at his home in Vermont, and Leper is definitely changed; he is very unpleasant and bitter with Gene, and seems to have been scarred in some way by his time in the service. Leper accuses Gene of causing Finny to fall out of the tree, and reveals that he left the service because he was about to be discharged for mental health reasons. Gene gets angry and attacks Leper for his comments, then apologizes and is too embarrassed to leave immediately. After lunch, Leper and Gene go for a walk, and Gene sees that Leper really has cracked up. Leper talks nonsense, and somehow it affects Gene, who yells at Leper to stop talking, and then runs away when Leper won't.