Oh yeah, he wasn't open about it but the war injured him literally and, even more, psychologically. I don't think he ever recovered. He was part of the lost generation that struggle so much in the 1920s. This part of him is more visible in his semi-autobiographical novel The sun also rises. I have to read Farewell to arms from him, which is set in the WWI.

Have you read Stoner by John Williams? I don't always enjoy American literature but this one was amazing! Currently reading his second book called Butcher's crossing.