It's funny, first partner-registration was created, to give legal rights to gay couples. Then a lot of not gay couples went for partner-registration too. Then marriage opened up for same sex relationships. And now we have both marriage and parter-registration, for all. And there is not much difference between the two.
And there is the option of making legal arrangements via a notary public. Less binding, and giving less rights too.
Lots of choices here, for all.