Scott Disick was banned from supporting his pal Rob Kardashian on the set of “Dancing With the Stars” because of an alleged tryst with contestant Kristin Cavallari. According to Life & Style, Disick — the longtime boyfriend of Rob’s sister Kourtney — and Cavallari “hooked up” in Las Vegas in 2009, before Kourtney became pregnant with Disick’s son Mason. “While Kourtney and Scott were on a break, Scott hooked up with Kristin,” a friend told the mag. Scott was also caught on a date with Cavallari in LA, the piece says. Meanwhile, Cavallari was spotted over the weekend in Chicago with her ex-fiancé, Bears quarterback Jay Cutler, at Public House.