The `Modern Family` actress - who has been dating Nick for more than two years - confessed to friends at the Met Ball in New York earlier this week she is now single after a period of fighting.
A source told the New York Post newspaper: "Sofia was confiding in friends at the ball that she and Nick have split. They have been fighting a lot recently and have been on the brink of splitting many times. It is not yet clear if they are over for good, but they are done as a couple for now."
Insiders claim it may have been the pressures of her newfound fame on `Modern Family` and a host on `Saturday Night Live` which caused them to break up.
Sofia - who turns 40 in July - recently said she first fell in love withNick because he was not intimidated by her looks or fame and seemed "normal".
She revealed: "The most important thing was that he was very handsome. But he was also very funny, talking s**t to me like a normal person."