Paris Hilton has her sights set spending "forever" with beau Benji Madden . "We talk about [marriage]. I'm so happy . I'm so in love. I know I want to spend the rest of my life with Benji, my boyfriend ," the 27-year-old heiress told David Letterman (watch above). "I know I want to be with him forever," she added. "If you saw us together, you'd understand." Madden, 29 – who said Hilton is " wife material " earlier this month – is briefly shown waving to his girlfriend from backstage of ...