In Boyne's The Boy in the Striped Pajamas, how does Bruno's experiences cause him to change throughout the story?

In The Boy in the Striped Pajamas, Bruno's experience in befriending Shmuel significantly changes him.

As the story opens, Bruno is unhappy.  He dislikes being in Auschwitz because of what he left behind in Berlin.  Bruno is incapable of moving past how he has no friends. After being so popular in Berlin, Bruno feels alone in Auschwitz.   Bruno is even intrigued at "the people in the striped pajamas" because he figures  they are having more fun than he is. However, when he makes friends with Shmuel, Bruno changes.  As his friendship with Shmuel grows, Bruno no longer pines for what he left behind.  He changes in that he now wants to stay in Auschwitz. When he hears of the plans to move back to Berlin, Bruno is saddened.  This is a distinct change from when he marched into his father's office and insisted that he does not feel "at home" in Auschwitz.  The full extent of Bruno's change is seen when he feels bad telling Shmuel that he will leave.  When they decide to embark on one final adventure, Bruno is excited, a stark change to how he was at the novel's start. In their final moments together, Bruno cannot remember the faces or names of his Berlin friends. He shows tremendous change in how he clutches Shmuel's hand, and tells him they are "best friends for life."  Bruno's friendship with Shmuel is an experience that profoundly changes him.