I like the idea that marriage predates our current legal and religious system, so anyone can describe themselves as married if they want to, and the other person(s) in that marriage as their husband or wife.
It would make the whole thing simpler if you could just refer to someone as your wife or husband, without the assumption of there being a legal contract.
However, I don’t live with Mrs MTG, so it would lead to a different assumption altogether if I said “I stayed at my wife’s house last night” or “My wife’s coming to visit tomorrow”.