When Nathan first came onto the show....I hated him. 'Right as Raynes' helped a bit for me, but I didn't really warm up to him till the snarky banter later in season 2 and early in season 3.
Come his death in season 3, I was really upset to see him go. And from what I hear, he will not be returning at any point in season 3. Adios, Stark