Patrick Mitchell, 43, of 1750 Grand Concourse, was arrested after the second fire Tuesday, and charged with two counts of arson and two counts of burglary, police said.
No one was reported injured in the fires at the woman's Graffing Place apartment, police said.
Mitchell deliberately ignited a fire to the apartment door of the former girlfriend at 5:53 a.m. Monday, Nassau police said. That fire caused damage to the door and hallway, and was extinguished by the Freeport Fire Department, police said.
Mitchell returned to the apartment 4 a.m. Tuesday and again started a fire "in the same location," police said.
An investigation had already been initiated by the Nassau County Arson Bomb Squad and Nassau County Fire Marshal unit after the first fire, police said.
Mitchell was to be arraigned Wednesday in First District Court, Hempstead.