Robert Pattinson and Kristen Stewart Wine and Dine in New York City

Before they hit the red carpet together at the Breaking Dawn—Part 2 world premiere, the Twilight stars were spotted celebrating a friend's birthday in New York City Thursday night with the likes of John Mayer, Sienna Miller, Tom Sturridge, Leonardo DiCaprio and Nicky Hilton.  "Rob and Kristen are definitely a couple," a source said. Pattinson and Stewart arrived separately to the event, but later headed to a nightclub together after finishing dinner at about 1 a.m.