Why does Ishmael begin to tell Esther about his past as a soldier? (chapter 17)

Esther attempts to win Beah's trust by patiently showing an interest in him without pushing him. She even uses reverse psychology by challenging Beah to win her trust before she will talk with him at length. She learns of Beah's interests through the school questionnaires and uses this knowledge to break down Beah's emotional barriers. She considers Beah a brother and consoles him in his most dismal emotional troubles. She cleearly wins him over.