In "The Scarlet Letter", how is Pearl both Hester's torture and comfort in life?Also, Which characters stayed true to themselves? Which did not?

I'm not sure that Dimmesdale does not remain true to himself ... it's just that it was very destructive.  This somewhat lengthy quote highlights that point:  " Mr. Dimmesdale was a true priest, a true religionist, with the reverential sentiment largely developed, and an order of mind that impelled itself powerfully along the track of a creed, and wore its passage continually deeper with the lapse of time. In no state of society would he have been what is called a man of liberal views; it would always be essential to his peace to feel the pressure of a faith about him, supporting, while it confined him within its iron framework."

Dimmesdale's self was intimately tied up with his sense of religion, supporting him in its unbinding "iron framework."  Just as Hester remained true to her freedom from the censure of the Puritan community, so Dimmesdale remained true to the framework that supported him. 

Many people find Hester a much more sympathetic, true-to-hserself character; I find Dimmesdale to be as true to his values as Hester, although the consequences of this loyalty are not at all admirable in many people's eyes.