The movie marks Barrymore's directorial debut.
Barrymore's publicist confirmed earlier this month the couple had broken up after dating for about a year.
A source told E! News Long is "distraught" about the split and has subsequently quit her roller derby flick.
"He couldn't stand working with her and not being with her," the insider told E!. "He's too upset."
Barrymore has appeared in the movies "ET: The Extra-Terrestrial," "The Wedding Singer," "Ever After" and "Music and Lyrics." Long's film credits include "Accepted," "Dodgeball" and "Live Free or Die Hard."