Inside David Letterman's Love Life
10/15/2009 AT 02:00 PM EDT
And, as friends and other sources reveal, that love life has always been both idiosyncratic – and messy.
While one source close to Letterman tells PEOPLE that Letterman's affairs – including an alleged liaison with his longtime assistant, Stephanie Birkitt – "pre-existed his marriage" to Regina Lasko last March, it is his marriage that Letterman will be working to shore up as he heads on vacation in the coming week.
Lasko, 48, who dated Letterman, 62, for more than 20 years and is the mother of his 5-year-old son, Harry, never speaks to press and is rarely photographed. She is "wonderfully nice" but "long-suffering because of the length of time Letterman dated her but wouldn't marry her," says one longtime Late Show insider. "She was crazy about him, so she put up with the situation."
Yet Letterman was always drawn to other smart, funny women as well – including Birkitt, 34. "Stephanie is sweet, goofy and quirky, which is a major lure for David," says the source, who has discussed both Lasko and Birkitt with Letterman. "She's a peculiar character and David is fascinated with peculiar women."
Still, a source close to the TV host, if forced to make a choice, Letterman will opt to shore up his marriage. "The truth is," says the source, "he's 24-7 focused on his wife and son."
For more on the Letterman scandal – including bombshell revelations about his alleged affair with Birkitt – pick up the new issue of PEOPLE, on newsstands Friday