After my glorious night of passion with Elena in the snowbound airport hotel, I flew home that afternoon. The house smelled of laundry and toast when I walked in. My wife met me in the kitchen with a tired smile, still in yoga pants and sports bra from that morning’s workout: slim, athletic, familiar. The children tackled my legs. Ordinary life closed around me like a warm coat. But I knew something had shifted in me. Tha...