What if she was living with this man and he had two children with her? Would she get the tax break for being a single mother? And what often happens with this "living together" nonesense? You have two people living together for years, sometimes one person has children from another man.
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.
I lived platonically for 6 years with a female roommate while we each saved money to buy our individual houses. No one gave birth.