Anyone who has been married for a long time starts to feel like a soldier surrounded by heavy casualties. In graduate school, a couple who married when we did failed to make it through a year. In my first job, we were one of four couples who got together almost every weekend; a few years later my wife and I were the only ones still together. Deep into our married life, five couples we knew, each together at least two decades, came apart in a single year, shells of separation bursting all around us. Like surviving soldiers, we like to think we were a little better prepared, maybe a little better suited for it. But we also know we’ve been lucky.