In The Absence of Men by Philippe Besson

It is the summer of 1916 and, with German Zeppelins on the skyline, the men of Paris are off at war. For Vincent, the sixteen-year-old son of a prestigious family, the tranquillity of the city sits at odds with the salons and soirees he attends. But, after an electrifying encounter with the enigmatic writer, Marcel P, draws Vincent’s desires out into the light, his ever-riskier liaisons with a young solider begin to shape Vincent’s future.

(Penguin Books)