Why does Isma decide to tell Eamonn of her family's history in Chapter Two?

Isma tells Eamonn of her family's history after she talks with Hira Shah. Hira tells Isma how she had first thought Isma had been mad at her until Isma had explained her family's history and the pain of her mother's death. Hira tells her that secrets fester, which pushes Isma to not keep this secret from Eamonn any longer.