Aren't there laws defining a "commonlaw" marriage as two unrelated, opposite sex adults living together for a specified period of time? If I remember correctly, under NC Law, you are legally married if you have been cohabitating for more than 6 months. I could be completely wrong however.
There doesn't appear to be any common-law provisions in NC state law. One would assume that with a law like this on the books, one wouldn't be needed.
I think it's more than just living in the same house. I think you pass the test if you have a joint checking account, maybe have both your names on an apartment lease or on a mortgage, etc...
NC has no common-law marriage. Obviously, such a law would be in contravention of this law. I wouldn't dare suggest NC doesn't have conflicting laws, but none that are this old.