At the end of every discussion Esther has with Beah, she always sternly tells him that, "None of these things are your fault" why does she say this to him?

Esther tries to convince Beah that his family dying and his war-time experiences were not his fault. Beah was a victim of circumstances that were beyond his control. I think that at this point, Beah is still confused and frustrated. Slowly Beah opens up to Esther and he is able to put his experiences in some kind of context.