At the end of the story, why does Gene go to the infirmary?
Gene goes to the infirmary several times during the 12th chapter in order to visit his friend, Finny. The first time he goes, it's to apologizes to Finny, but Finny "thrashe(s) wildly in the darkness," vainly struggling "to unleash his hate against Gene. Instead, Gene is only about to whisper "sorry" to his once best friend.
He returns the next day to bring Finny clothing. He and Finny barely speak as Finny describes that he's been trying to find a branch of the military to join, but has had no luck.
His final trip to the infirmary is after Finny's surgery to reset his leg. It's supposed to be a simple surgery, but somehow during the surgery his heart stops, and Finny dies. Dr. Stanpole tells Gene that a piece of the bone marrow must have entered the blood stream and blocked the heart.