To Paradise by Hanya Yanagihara

From the author of the modern classic A Little Life, a bold, brilliant novel spanning three centuries and three different versions of the American experiment, about lovers, family, loss and the elusive promise of utopia. In an alternate version of 1893 America, New York is part of the States, where people may live and love whomever they please (or so it seems). The fragile young scion of a distinguished family resists betrothal to a worthy suitor, drawn to a charming music teacher of no means.