I think that the friendship between both boys can be described as real. Their friendship is one that cuts through social distinctions, religious distinctions, and historical conditions. Both boys fill a need for companionship in the other. It is for this reason that their friendship is real and valid. In displaying a friendship that transcends existing conditions, one is reminded of what can be. This is where the ultimately real quality of the boys' friendship exists.
In one respect, their friendship is real because both boys mirror one another. This is seen in the most literal of senses when Bruno has to have his head shaven because of lice. This can also be seen when he accompanies Shmuel on their "adventure" as Bruno crosses the fence. Symbolically, their friendship is real as they both confess to the other that neither of them "like" Auschwitz. Bruno and Shmuel recognize at that moment that their friendship is the only thing sustaining them through the horror of Auschwitz. When they are herded into the gas chamber together, the midst of terror is where their friendship achieves their greatest significance. When Bruno tells Shmuel that he is his "best friend for life," when fear and terror grip both of them, it is a reminder as to how real their friendship actually is. In the end, this becomes the word to describe their friendship. Both boys actually die in one another's arms, with only the comfort of the other to offset the terror of death in the gas chamber. Their friendship carries both boys beyond the fear of a lonely death in the Holocaust. This indicates how real their friendship was.