John Weir’s “Your Nostalgia Is Killing Me,” alternately identified as “Short Stories” and “Linked Stories” — 11 in all — is wise, often funny, and poignant yet unsentimental testimony from a narrator named John Weir, whose formative life experiences were his bullying as a youth and the death of “half the people I knew when I was twenty-five” during the worst days of New York’s AIDS epidemic.