David Paterson has a new mystery girlfriend. When the ex-governor and current WOR-AM host popped up at a party in Syracuse Saturday celebrating the opening of a brewery and restaurant, guests, and even the party planners, wondered why. Sources tell us Paterson was at the 800-person Gordon Biersch bash with his new lady. “Turns out he was there to visit his lady friend, not because of the event,” a source says. “He has a steady girlfriend . . . it is an exclusive thing.” We exclusively reported Paterson and his wife, Michelle, separated after 19 years in September. He’s headed to Seattle today for a protest by the National Federation of the Blind over Amazon’s push to put Kindle e-books in schools.