How does Peter becomes an example of sacrifice?

Peter appears to have given up on himself. His wife has left him and his children died long before the crisis, and he seems to feel the need to care for and protect everyone but himself. He is a sad person, and seems to get more tired and depressed as the story goes on. The only thing he has to live for is Miranda's mother, but she has to be focused on her own family now. Peter chooses to sacrifice himself to help others instead. His death is heroic but also very sad.