Halderman lived until recently with Stephanie Birkitt, 34, who had previously been a personal assistant to Letterman. Public documents indicate that Birkitt and Halderman lived together in Norwalk, Conn., from August 2005 to August 2009. Birkitt now has an apartment on Manhattan's Upper West Side.
Halderman has been married and divorced twice, according to public records. He had two children with his second wife, and has three stepchildren. His ex-wife won custody of their children and now lives in Colorado.
Divorce records show that Halderman was ordered to pay $6,800 a month in alimony and child support starting May 1, 2004.
Letterman, 62, confessed during a taping of "The Late Show" for broadcast Thursday night that he had had sex with members of his staff.
Letterman revealed to the studio audience that he'd received a package three weeks ago containing a threat to reveal those indiscretions if he didn't pay up.
Halderman has been suspended from his job as the investigation continues.
His colleagues were dumbstruck by the charges against him. Halderman has been described as a consummate professional who was well-paid and highly regarded.
According to a source close to Letterman, all the liaisons Halderman was allegedly going to reveal regarding Letterman occurred before the comedian's March 2009 marriage to Regina Lasko, with whom he has a son, Harry Joseph Letterman.
This is not the first extortion plot alleged to have targeted Letterman. In 2005, Kelly Frank, who worked as a handyman on Letterman's Rocky Mountain ranch in Montana, was arrested for allegedly plotting to kidnap Letterman's then-16-month-old son. Frank pleaded not guilty but got 10 years in jail for overcharging Letterman.
Letterman, who was a longtime bachelor after his first marriage ended in divorce in 1977, has had at least one relationship with a co-worker in the past. Merrill Markoe, a comedian and author who was his longtime writer, was his girlfriend in the 1980s.
Markoe reacted to the news of the extortion plot on her blog, saying, "As you can imagine, this is a very emotional moment for me because Dave promised me many times that I was the only woman he would ever cheat on."
And former intern Holly Hester told TMZ.com that she had had an affair with Letterman but that he called it off because of the difference in their ages.
ABC News' Eileen Murphy, Michael James, Lindsay Goldwert, Brandon Bodow and Richard Esposito contributed to this report.