Also, marriage is not legally defined as a covenant with God, only as a contract between a man and woman in which they live together (genders involved have been updated/stricken in recent times, of course).
Eh? No, marriage isn't legally defined as a husband and wife (or two partners, or whatever) living together, dun. Pretty sure it hasn't been for quite a long while, even, if ever so far as the US court systems are concerned.
It
is a legal contract, but it's one that makes the pair a single entity for many/most legal concerns, including taxation (if not opted out of, which is more expensive). Relatively similar to a joint partnership business, iirc, where all involved are responsible for any/most debts, court concerns, etc. Doesn't really have much to do with where they're living, though. Just how they're filing.
And yeah, strictly speaking it has fuck all to do with the religious conventions. It's a legal contract with primarily financial concerns and a side of property/guardianship/etc. It's honestly kinda' sketchy as hell we
do limit it by gender, because that's adhering to a religious tenant more than anything that has to do with the legal arrangements involved. Those arrangements don't really have much of a damn to give about what's banging (or not) what with what sort of dangly (or not) bits, they care whether or not they got your ass in a joint and several agreement so far as paying your taxes and criminal/civil liability are concerned.