Why does Hester feel she is to blame for Dimmesdales poor condition?

Hester feels responsible for Dimmesdale's poor condition because she believes her decision to keep his identity as Pearl's father a secret contributed to his suffering. She believes that had she revealed the truth earlier, Dimmesdale may have found relief from his guilt and despair sooner. Hester bears the burden of their shared secret and feels responsible for the consequences that Dimmesdale endures.