Played by Jeremy Sisto
Billy is Brenda's younger brother, a bright but disturbed young man. He's a diagnosed manic-depressive who, as Brenda says, "always seems to pick the holidays to go off his meds." In the past, Billy — who could be charming one moment and hostile the next — was highly possessive of Brenda, who seemed to have made taking care of him her life's work. As children the two of them were nearly inseparable, and as adults it was Brenda who Billy turned to when he felt overwhelmed.