Simpson married Fall Out Boy bassist Pete Wentz on May 17, 2008. The two were first seen together in late 2006; initially they denied being in a relationship, although there was much speculation about this. In an interview for OK! magazine in late 2006, Simpson denied the speculation, while in an interview with Pete Wentz on Ryan Seacrest's American Top 40 live, Seacrest asked if Wentz and Simpson were "on" or "off", and Wentz laughed and said "off". In a Rolling Stone photo shoot, however, Wentz and Simpson took a picture together for the opening of Wentz' bar, Angels & Kings, and were labeled as a "couple".

Eventually the two began to acknowledge the relationship. In mid-2007 Wentz spoke about their relationship to InTouch magazine, saying of Simpson that "I have never met somebody who makes me feel the way she makes me feel", although he denied rumors of engagement. Simpson has since discussed their relationship in a number of magazine interviews, including the Septembe