I totally agree that the writers shafted Nate after Season 3. I never understood why they were so determined to go back to Derena, after it was established that Serena could never be comfortable with herself when she was with Dan.
Season 3 was messy. I liked her with Carter but they just got rid of him like he never mattered. Then they FINALLY do Serenate, but somehow, bring Dan back into the equation even though he fell for Vanessa.