Depends on the state you live in, there's only a handful of states that actually recognize common law marriages. Those who do, there is a strict criteria to qualify for one. It's more than just living together.
One thing people don't realize with a common law marriage is that if you have a legit one that the state does recognize, if you split.. you do actually have to get a divorce because on the state is actually recognizing, you have many of the same legal benefits a traditional marriage does for assets.
My grandparents had a common law marriage in Michigan when they were recognized here (they no longer are) and since they had assets, had been together 30 years and had minor children when they split, they had to get a divorce.