How did the loss of Milly affect Lassiter? He talks about traveling and going to the "bad." What did this mean and how is this connected to the loss of his sister?

Lassiter's loss of Milly, his sister, affected 18 years of his life. In his search for her, he traveled into areas of the country known to be rough and he had to become a gunman to survive. His survival instincts follow him, and he cannot let go of his hate toward the Mormons who hurt his sister. His entire personality is wrapped up in Milly's disappearance and death. Not only did her lose her, but he also lost his best friend and his mother and father.