Around 40 percent of people who marry eventually get a divorce. Almost half of children are born to unmarried women. The number of close friends Americans report having has been on a steep decline since the 1990s, especially among men. Millions of us are growing old alone. We are living out a radical experiment in how we live, love, parent and age — and for many, it’s failing. That’s partial context, I think, for the recent burst of interest and media coverage of polyamory. People want more love in their lives, and opening their relationships is one way to find it. A poll from last year found that one-third of Americans believe their ideal relationship would involve something other than strict monogamy. But polyamory, for all its possibilities, isn’t right for many, and it doesn’t have that much to say about parenting or aging or friendship. As radical as it may sound, it’s not nearly radical enough. It’s not just romance that could be imagined more expansively. It’s everything. “If this is such a significant relationship in my life, why is there no term for it?” wonders NPR’s Rhaina Cohen about a relationship that transcends the language we have available for friendship. Her forthcoming book, “The Other Significant Others: Reimagining Life With Friendship at the Center,” is a window into a world of relational possibilities most of us never even imagined existed. It’s a call to open up what we can conceive of as possible. Some of these models might appeal to you. Others might not. But they all pose a question worth asking: What kinds of relationships would you want in your life, if you felt you could ask for them?