I’m a divorced dad in my mid-fifties. My only child is a college student who comes home most weekends. A friend of his is staying the weekend with him. None of that was unusual—Brad came home most weekends to hang out with his girlfriend, and his buddies would often come along. It was late Friday night when I saw his headlights coming up the driveway. I’d been a bachelor for a few years. I was sitting on the couch in just...