1_From my point of view, Shmuel must think that Bruno is different from the other boys he knows “but there are a lot of us – boys our age, I mean- on this side of the fence. We fight a lot of time though” (The Boy Striped Pyjamas, chapter 10, page 110). Shmuel must realize that both of them are alone and they have a lot of things in common.
2_As Shmuel does not have anybody to talk or play with, he thinks that Bruno could be the friend that he needs. Also, because Bruno has been so nice with him and he hates Auschwitz as well.