Now we know why Ben Affleck and David Fincher were doing lunch in Los Angeles this week. Deadline.com reports that Affleck is in negotiations to star in “Gone Girl,” Fincher’s movie based on the best-selling book by Gillian Flynn. Affleck would play a husband who is implicated in his wife’s disappearance on the couple’s fifth anniversary. Oscar winner Reese Witherspoon is one of the producers of the movie, but apparently she will not play the female lead. If Affleck ends up doing “Gone Girl,” it might mean that he’ll push back production of “Live by Night,” the movie based on the Dennis Lehane novel that Affleck plans to direct and star in. Though he clearly seems to enjoy directing — “Argo” won best picture, after all — Affleck has not abandoned acting. He’s one of the stars of “Runner Runner,” an action drama costarring Justin Timberlake, which comes out in September.