A soldier speaks in the moment of leaving. He has left his wife and is heading off to war, and he says it plainly, almost in shorthand, as if he can't afford to linger on the goodbye. The title, "Shooter," suggests he is the one who will do the killing, which makes what follows more unsettling.
His real focus is on what comes after. He expects to come back, but not unchanged: he will return "with visions" that will "nest" in the night. A nest is a homely word, something living and settled, and here it's turned into something that will take up residence in his mind. Those visions will then call him up "from a horrible dark bed," so even sleep becomes a place he can't rest.
The mood is bleak and quietly dreading. The lines are short and spare, and the speaker sounds resigned rather than angry. He seems to know the war will follow him home, and that the harm will reach him at night, long after the fighting ends.