She could try to sue you, but you would be able to object that the North Carolina courts don't have personal jurisdiction over you. Also, if he has a long pattern of infidelity, it would be difficult for her to establish that the marriage would have survived but for your conduct.
In my experience, a guy who cheats on his wife will also cheat on his girlfriend, and if his girlfriend marries him she becomes his wife... and we already know he cheats on his wife.

