Matthew Broderick is allegedly having an affair with a 25-year-old youth counselor he met at a bar earlier this year. Eyewitnesses claim to have seen the two together numerous times while Sarah Jessica Parker was in LA filming Sex and the City: The Movie, according to Star:

Sources say the woman felt conflicted with her relationship with Matthew, whom she nicknamed "Matty Cakes." She tried to end it, say insiders, but that didn't happen and over the next month ? when Sarah Jessica was filming Sex and the City: The Movie in Los Angeles ? multiple eyewitnesses say they saw Matthew make late-night visits to the other woman's apartment building.
During one tryst, they arrived at her friend's apartment after a night of heavy drinking, says a source. She dragged Matthew into the friend's bedroom, then shut the door. "A half hour later, Matthew opened the bedroom door, mumbled 'Well... 'bye!' and walked out. The friend found her passed out on the bed in her panties."

I'm surprised Sarah Jessica Parker hasn't caught Matthew Broderick sticking his penis in a variety of things besides her. Like a ham sandwich. Or, let's be frank, a blender.
(Source)