In Chapter 17 of The Scarlet Letter, Dimmesdale and Hester agree to meet in the forest. When they meet, they realize how much they have changed, and they talk about the past. However, they eventually arrive to Hester's secret, which is the purpose of the meeting.
Hester reveals to Dimmesdale that Chillingworth is her husband. Dimmesdale is initially angry, but he soon forgives Hester. He also realizes that this explains the complex and contradictory feelings he has had towards Chillingworth in the past.