RICHARD Wiese, who made People magazine’s list of Hottest Bachelors in 2003, is officially off the market. The host of ABC’s “Exploration with Richard Wiese” – who was JFK Jr.’s fraternity big brother at Brown University – is marrying South African beauty Nicole “Nicci” Young tomorrow in Southampton. The happy couple met four years ago when Young, 38, became executive director of The Explorers Club, where Wiese, now 48, was serving as its youngest-ever president.