At least in the past there were state laws about "common law" marriage. I don't know if they still exist, but I'd hope people would be smart enough to make legal arrangements in case of things like untimely death, health emergencies, property disiposal in case of break-up, etc. I have a nephew who has been living with a woman for many years. I admit I've not asked him what arrangements he may or may not have. But they don't have children, so I expect it's not needed as much as if they did.