https://www2.gov.bc.ca/gov/content/life-events/divorce/famil...
Only a few states have something like the common-law 'marriage' you picture - but it's a really high bar.
There needs to consideration AND usually clear intent to marry (w/ nuance of course);
You can't simply fall into this by happenstance because you cohabitate for {n} amount of years.
California does have a (ever barrowing) Marvin Action.
But it's an incredibly high bar and not family court
You need to prove that essentially a contract exists between the parties; * e.g. consideration *
https://www.wgslawfirm.com/family-law/divorce-mediation/2025...
That's not some "oh, we live together, and under old-timey understandings that means we're married" requirement. That's publicly making a pattern of referring to each other as your spouses, often including at least some public documentation. Common law marriage is much more about protecting people who failed to dot their 'i's and cross their 't's when registering their marriage than it is about surprising a breakup partner with divorce precedings.
For the record I had heard this from a lawyer, not some random person.
My father's last "marriage" was like this. After several divorces he was dead set on never getting married again, made sure only his (or her) name was on any purchases, and made sure his friends knew the situation. After a messy breakup where he discovered she had been diverting money for drugs and hiding bills, her lawyer managed to convince an Alabama court to find a common law marriage. Not long after she ended going to prison for arson after setting aflame some of my father personal and real property in piques of spite. I think those felony convictions happened prior to or at least concurrent with the common law marriage proceedings.
It isn't true in California, it appears. It is true in a number of other places worldwide, Australia in particular.
Even in Australia, a de facto relationship – in which partners have a right to a property settlement upon separation – requires more than mere cohabitation of sexual/romantic partners. However, in practice, relatively few long-term cohabitating partners will be found not to be in a de facto relationship.