It looks like BlackBook chief Ari Horowitz‘s single days are behind him. The magazine’s CEO, 41, recently proposed to his longtime girlfriend, NYU graduate Laurel Cummings, 24. “We got engaged this weekend out at our kite-surfing shack in Amagansett,” Horowitz tells Page Six. Cummings is currently an assistant to “Saturday Night Live’ producer and “Late Night With Jimmy Fallon” announcer Steve Higgins.