The passage is as follows:
We all had the same medals, except the boy with the black silk bandage across his face, and he had not been at the front long enough to get any medals. The tall boy with a very pale face who was to be a lawyer had been lieutenant of Arditi and had three medals of the sort we each had only one of. He had lived a very long time with death and was a little detached.
This statement suggests, especially as the young man has more medals than the others, that he spent a long time on the front in World War I. Because he has experienced so much death, he seems to be shell-shocked, as indicated by the understated words being a "little detached." (Today, we call this shell shock PTSD.) However, the narrator, usually taken to be Nick Adams, then goes on to say that all of the wounded soldiers are all a "little detached." This observation and the deadpan, flat style of the narrative suggests that war trauma has shut most of these men down emotionally: they have switched off their emotions because they are unbearable. This makes the major's highly emotional response to the death of his wife all the more surprising.