3x17, The Inglorious Basstards.
Wow, that was a though one because I absolutely LOVE 3x10/3x11 storyline-wise, but this episode was the best Serenate episode for me. For once they were together and happy and I can see Serena planning on surprising Nate for his birthday since they were little kids. I can see how much she anticipated for this moment (she could have helped when he was with Blair, but it wasn’t the same) and how much she wanted it to be perfect for him. I think the show failed in showing us Serena’s side of the story but not in this episode. You cannot unwrite her face. She’s so in love she doesn’t even know how to behave herself. Also, THOSE LAST SCENES. It’s my shipper dream, tbh.
"Seriously? Best birthday ever".