I don't know how it is in other places, but in Vancouver, if you cohabit for a number of years, you are subject to the same stuff as if you were married couples. I can't remember the details, forgive me, busy work day.
Spread the word!
https://apeopleschoice.com/common-law-marriage-in-california...
You can also file married income taxes if you are legally married in your state of residence. In fact, if you didn't it probably would be considered tax fraud.