Seems to be that he's realizing his view of things was small (my world a bubble), and "she" came along and enlightened him to bigger things. And he isn't the only one in a bubble, it's everyone (my brother's was too)~ his brother is everyone, humanity. His brother sees what has happened to the narrator and says "why have you poisoned my brother's cup" but the narrator knows he has been shown his bliss, and someday so too will his brother.
Seems to be that he's realizing his view of things was small (my world a bubble), and "she" came along and enlightened him to bigger things. And he isn't the only one in a bubble, it's everyone (my brother's was too)~ his brother is everyone, humanity. His brother sees what has happened to the narrator and says "why have you poisoned my brother's cup" but the narrator knows he has been shown his bliss, and someday so too will his brother.