Home vs. not home
The sense of home is synonymous with a sense of comfort and safety. Baker's sense of "not-home" corresponds to discomfort and fear. This is the case for the latter part of Book One. Frederick is forced to deal with injury and war wounds, as well as Italians who consider him an outsider. The imagery there is of darkness and dampness as Frederick and the other ambulance drivers await action on the war front. There is obvious danger in the mortar shells that fall all around them as they wait in the brickhouse, falsely sheltered by the building. The location is telling, down by the river in the low-lying areas. Even the dugout, really a brickhouse that was being used for shelter is significant in that is is usually a source of great heat as the clay is baked into bricks in the large ovens by the river.
Contrast this with the early part of Book One, in which Frederick first meets and courts Catherine, and he consumes wine and vermouth with his enlisted mates at the mess. He is free to visit the brothel and spend time with Rinaldi. This is a life of leisure; he does little work for the army and gets to have fun almost all of the time in the town. This is only ignorant comfort, however. He does not care about the war, and he lacks the inner peace and prosperity that will come in Book Two. All the fun he has in town is just playing around. It is certainly fun for him, but not fulfilling.
The truly comforting setting for Frederick however, is in Milan. He is far displaced from the war and battle in the hospital. He is waited on by the staff and excepting the pain from his wounds, has little if any discomfort. He is afforded the luxury of seeing Catherine, whom he finds himself in love with all of a sudden. It is as if being injured has affected a change in his psychology that allows him to love her. Frederick's level of control is articulated when he states, "When I saw her, I was in love with her" (Farewell 91) and later, more acutely, "God knows I had not wanted to fall in love with her. But God knows I had." (Farewell 93) This is not the fake love that he feels for her as they play their "rotten game", this is true love according to Frederick.