Why do you think Paul feels disillusioned and unhappy after his encounters with the French girl?

Love and war are frequently starkly contrasted in literature: love produces birth and other emotions of re-birth, while war produces death and its attendant mortal emotions. Paul hopes to separate love and war--he wants the brunette to deliver him from "war and terror and grossness, in order to awaken young and happy." However, the brunette is interested in Paul only if death is around the corner for him. When she learns he is going off on leave, he is no longer a "'pauvre garçon'" ("poor boy"), but simply another man. She is sold on the romantic notion of war, and love for her is possible only if Paul is an idealized, heroic soldier.