SO this, in the end, is what love is.

Former Justice Sandra Day O’Connor’s husband, suffering from Alzheimer’s disease, has a romance with another woman, and the former justice is thrilled — even visits with the new couple while they hold hands on the porch swing — because it is a relief to see her husband of 55 years so content.

What culture tells us about love is generally young love. Songs and movies and literature show us the rapture and the betrayal, the breathlessness and the tears. The O’Connors’ story, reported by the couple’s son in an interview with a television station in Arizona, where Mr. O’Connor lives in an assisted-living center, opened a window onto what might be called, for comparison’s sake, old love.

Of course, it illuminated the relationships that often develop among Alzheimer’s patients — new attachments, some call them — and how the desire for intimacy persists even when dementia steals so much else. But in the description of Justice O’Connor’s reaction, the story revealed a poignancy and a richness to love in the later years, providing a rare model at a time when people are living longer, and loving longer.

“This is right up there in terms of the cutting-edge ethical and cultural issues of late life love,” said Thomas R. Cole, director of the McGovern Center for Health, Humanities and the Human Spirit at the University of Texas, and author of a cultural history of aging. “We need moral exemplars, not to slavishly imitate, but to help us identify ways of being in love when you’re older.”