I've said it for years decades a half-century: except for obvious legal issues, the relationship between two (or three, or four) individuals is none of my business, or yours, or the government's.
I'd maybe like to see renewable cohabitation permits for, say, five, ten, (or fifty) years to cover those legal issues. I'm sure the divorce rate would drop to near-zero since there would be an automatic "out" and chances are couples (of either gender) would resolve their issues if they knew there was that automatic "out" at some point in the future.
What set me on this path of half-assed thinking was that back in the sixties, a rancher came to town (Boulder, CO) to marry his horse. Got some people to thinking, which was his purpose, of course.