For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
We see Paul's talents – he can survive. He reads people and is able to suck up his pride in order to survive various hardships and just get through to another day. By the time Paul begins to define "home" as the Front instead of the house he lived with his family, it should be clear that Paul's fate is sealed – he will die. Act I ends around the end of Chapter Three and middle of Chapter Four.
Act II
In the middle of Act II, characters realize what their fate should be. Paul becomes fatalistic right about the middle of Chapter Six and accepts that he will probably die. At the end of Act II, the main character is further away from his fate than he ever will be in the story. Ironically in this case, that end of Act II happens when he is sent home on leave to recover. But he swiftly moves himself back to the Front after a brief glimpse of a freedom he can no longer handle. The Front makes him alive inside by virtue of his being so close to death.
Act III
All of Paul's friends die. Finally, Paul dies and achieves peace in death.