What transformation did Roger Chillingworth experience in Chapter 11 and why?

Chillingworth, having figured out that Mr. Dimmesdale is the true father of Pearl, goes on a subtle campaign to hurt the minister as much as possible. Revenge consumes him to the point that he can only focus on causing the other man pain. Chillingworth's revenge physically and emotionally changes him. He can think of nothing else in his life. He begins to shrivel and age quicker.