Unfortunately, it is the narrator's failure to give a sign of mercy to Doodle because of his own shame that leads him to desert Doodle to his death. The narrator's pride has been cracked, and he recognises that no words are able to "solder" that crack together again.
The tragedy of this story is that the narrator is unable to accept his brother for the unique and special individual that he is and feels that he needs to transform him into a more socially acceptable individual because of his own sense of shame at his brother. It is this that leads to Doodle's death.