In chapter 15 what has happened to Schmuel when Bruno doesn't defend Schmuel, and Lt. Kotler takes Schmuel away again?

Bruno felt
terrible about denying their friendship. 

"He had
never felt so ashamed in his life; he had never imagined that he could behave so cruelly. He
wondered how a boy who thought he was a good person really could act in such a cowardly way
towards a friend." (pg 174)

Because he felt so bad
about it, it really hurt when he didn't see Schmuel for almost a week.  Bruno was
convinced...