Activist Christine Marinoni

Cynthia Nixon's mystery girlfriend is a mystery no more.
Education activist Christine Marinoni is the lady who captured the heart of the "Sex & the City" star, sources tell us.

Friends say Marinoni, the New York City director of the Alliance for Quality Education, and the Emmy-winning actress fell in love while fighting for increased funding and smaller classes in public schools.

"They share a strong commitment to improving the lives of children in the city and the state," said a friend.

Nixon, who sends her two children to public schools, has stood shoulder-to-shoulder with Marinoni at several Alliance events. Before heading up the Alliance's downstate branch, Marinoni was director of the Parent Organizing Consortium, a citywide grass-roots group.

In 1996, she and a partner opened Park Slope's Rising Cafe, described in the Lambda Line newsletter as a "lesbian-owned and -operated business" where people can "hear or even make poetry and music, meet friends for coffee or beer." The cafe has since closed.

Nixon and Danny Mozes, the father of her children, split in June 2003 after 15 years together. Her romance with Marinoni is said to have blossomed last January.

Friends say Nixon divides her time between Marinoni's pad and her own upper West Side apartment, where her children live and where "Christine sometimes comes along on playdates," says a pal.

Marinoni didn't return calls. Nixon's reps declined to comment.

wait, so the black chick in the white shirt is her girlfriend? she's pretty, but wow - cynthia really let herself go.

Anxiety said: