How does Dimmesdale react the the truth that Chillingworth is Hester's husband and what does that say about chillingworths actions?
When Hester finally reveals to Dimmesdale who Chillingsworth is, he finds himself experiencing a number of intense emotions. First he is furious that Hester has waited so long to tell him, wearing a frown so fierce the author comments that Hester has never seen one quite so black. However, this fury does not last long, and Dimmesdale collapses onto the forest floor mourning his inability to listen to his gut feeling regarding the physician's ill will toward him. When Dimmesdale blames Hester aloud for keeping him in the dark for so long, she finds herself desperate for his forgiveness, flinging herself into the leaves next to him. She frantically pulls him in for an embrace she hopes will alleviate his obvious pain. She feels as though she can bear any punishment, but Dimmesdale's disapproval. After a time he tells her that he forgives her. He then faces a comforting realization, there is someone who has committed a far crueler and greater sin than he and Hester, Chillingsworth. Chillingsworth was deceitful, he led Dimmesdale to believe that he only had Dimmesdale's best interest at heart, but he really was acting out an extreme form of revenge. Chillingsworth's cruelty allows Dimmesdale to briefly feel less pain and guilt.
When Hester finallly tells Dimmesdale about Chillingworth's true identity, Dimmesdale runs the gammot of human emotion. He initially does not handle it well at all. When she first introduces the name of the man who is her husband, Chapter 17 says, "Never was there a blacker or a fiercer frown than Hester now encountered."
This angry posturing doesn't last long, though. He soon falls to his knees on the forest floor, saying he should have known it and felt it in his guts all along. He then follows this by blaming Hester for allowing him to be in so much pain and in the clutches of the enemy for so long, just by keeping her silence. This drives Hester near madness. She can handle anything but Dimmesdale's disapproval. She holds the weakened, sickly man as a hug-hostage until he finally forgives her.
Dimmesdale finally realizes that, although he is plagued with guilt, he finally knows someone whose sins are worse than his own - Chillingworth. He and Hester face their lowest low, but they face it together.