"The Forgotten Soldier" by Guy Sajer. Account of a Wehrmacht soldier fighting on the Eastern Front in WW II. My 45+ year old copy is finally falling apart. Can't tell you how many times I have read it during that time. Bought it when I was 14.
I've got it on the shelf downstairs; been a long time since I read it last. Now I have to add it to the list of stacked up books I need to get to.