Celebrity | David Letterman Galpal Cheated on Halderman With Dave Stephanie Birkitt was still seeing Letterman until last fall, sources say By Evann Gastaldo Posted Oct 6, 2009 10:58 AM CDT Copied Attorney Evan L. Lipton, right, stands with his client, Robert J. Halderman, center, at Manhattan Supreme Court, Friday, Oct. 2, 2009 in New York. (AP Photo/Pool, Marc A. Hermann) The story of David Letterman’s twisted love triangle with alleged extortionist Robert Halderman continues to unfold. Former Late Show staffer Stephanie Birkitt was still sleeping with Letterman even after moving in with Halderman—and as late as last fall Birkitt and Letterman went hiking together, sources tell the New York Post. Birkitt—whom Letterman offered a job as his personal lawyer last year—told Halderman she was simply Letterman’s “best friend.” Though Halderman and Birkitt stayed together until last month, sources say things began to fall apart when he read her diary—and learned of her continuing affair with Letterman—in December. He allegedly began his extortion scheme by dropping off a screenplay outline about a talk-show host brought down by an affair in Letterman’s limousine, prosecutors say. Read These Next New Fox star, 23, misses first day after car troubles. White House rolls with Trump's 'daddy' nickname. Man accused of killing his daughters might be dead. Supreme Court ruling is a big blow to Planned Parenthood. Report an error