In 1998 Haddon started dating actor Christian Slater. The couple married on 12 February 2000, and have two children, Jaden Christopher (born 6 April 1999) and Eliana Sophia (born 15 August 2001). They announced their separation over Christmas 2004, while Slater was performing in a stage play of "One Flew Over the Cuckoo's Nest in London's West End. They officially separated in 2005 and divorced in November 2007.
In 2003, Haddon was arrested at about 7 a.m. for misdemeanor domestic battery against then-husband Christian Slater at the Hard Rock Hotel & Casino while on a trip to Las Vegas. According to the police report, she had thrown a glass at him during a 6 a.m. argument in their suite. Slater was treated at the Desert Springs Hospital while Haddon was booked into the Clark County Detention Center and released after 12 hours and posting bond. Slater's wound required 20 Stitches to close.
On July 25, 2009, Haddon married actor Marc Blucas.