Kisses, even the ones that don’t happen, can be the trace of what’s constant when life changes. In childhood, when what seems to define everything is competition—for style, for knowing, for experience—a kiss is the first first. When a girl’s father moves out and chooses a new family, a kiss on the head from him may be the trace of constancy that she wants most.Later, such things take on a different flavor. Sometimes the kiss she wants...