I'm making this about me, so feel free to skip past this.

I've been married for 26 years, which means I'd only have 10 more years with my wife, which would take us almost into retirement. That's not near enough. We're meant to have at least another 25-30 to take us deep into our 70s, becoming grandparents and seeing out that whole stage of life.

No guarantees in life, obviously, but there's no way to plan a backup "life partner". Half of the two people with that specific shared life experience is gone, it's an unfillable hole.