Sophie's Choice by William Styron

This is a very sad story.  The narrator, a very young man who is trying to become a writer, meets a young woman and her boyfriend after World War II.  The woman, Sophie, is from Poland and survived a concentration camp.  The boyfriend, Nathan, is a charismatic individual with mental and emotional challenges.  The narrator, Stingo, becomes very involved with this couple and their story.  The book is written in the perspective of Stingo looking back in the past.  The plot eventually hinges on a decision that Sophie made when she first entered the concentration camp.  It is an excellent read.