They see each other on Christmas, exchange pleasantries and walk away. Neither questions why the other is walking through Central Park when they should be with their family. But then Blair calls Dan and asks if she can come over, and they have Christmas dinner together. Or, they try in any case, but they burn the stuffing and the potatoes are all runny and the ham tastes weird. So they eat animal crackers and hot chocolate instead.
They kiss on New Year's. They were alone together and drunk and it was midnight and what the hell, right? And they spend the night in Blair's bed and wake fully clothed and vow never to speak of it again.
Blair is back with Chuck by Valentine's Day, but Dan gives Blair a valentine anyway. It doesn't have his name on it, and he isn't around to watch her smile and he doesn't see her tuck it away to admire later.
Dan stops getting Gossip Girl blasts sometime in July, when Gossip Girl shows everyone a video of Chuck and Blair making out on some beach. And he vows to forget the brunette vixen who has, for some inexplicable reason, become the inspiration for his latest attempt at a novel.
In August, Chuck cheats on Blair with some blond tramp in a seedy hotel in Brooklyn and Blair finds them there so she runs to the closest place she knows. She spends the rest of the week there with Dan, who has, sometime during the course of that week, become her errand boy.
Two weeks later, Chuck proposes and Blair cries and she accepts. Dan hears this through Serena, who's helping plan the wedding. When he runs into Blair, she winces as she tells him the wedding is going to be on New Year's. She says, apologetically, that Chuck picked the date and, how could she say no when she loves him and he had this fantastic idea for the line 'you may kiss the bride' to happen just before midnight so they can kiss exactly on midnight. And she goes on to say that it's the most romantic thing he's ever done and Dan can't think of anything else but when he kissed her on New Year's and all he wants to do is kiss her now. But he doesn't. He just wishes her well and walks away.
On Halloween, there's a Masquerade ball at Chuck's hotel and Dan's invited. He goes, more to torture himself than anything. And he spends the first half of the ball trying to find Blair. Once he finds her, he talks to her for a good hour and a half because he doesn't tell her who he is and she's too curious to let him leave without knowing. But then Chuck appears and he slips away unnoticed.
In November, Chuck forgets Blair's birthday, and Blair spends the day at Dan's, where they bake a cake and have ice cream and watch Breakfast at Tiffany's.
They continue the Thanksgiving tradition, and Blair and Dan and Chuck have dinner with Nate and Serena again. Only this year, Dan invites Jenny, who brings Eric. And Chuck says something stupid so Blair kicks him out and Serena and Nate get into a fight and Jenny runs off crying because of Chuck and Eric goes off to comfort her. So somehow, it's just the two of them, and Blair breaks down and Dan holds her while she cries until Serena comes back.
Christmas again, and Blair spends it with Dan. Chuck was supposed to take her out—they were supposed to have a magical night, so she says—but he had to work and she didn't want to be alone. They have an honest talk for the first time since New Year's, and they acknowledge that something is different. But neither one says what they're feeling and Dan doesn't give her the diamond necklace he saved up the money for all year.
The morning of Chuck and Blair's wedding—New Year's Eve morning—finds Dan waking up to a frantic knocking at his door. It's Blair, and she's wondering where her diamond bracelet is—the one she had on at Christmas—she says she needs it for her wedding. Dan, feeling sick inside, helps her look for it and, somehow, in the process, she finds the necklace. Blair starts to cry.
So Dan, holding the necklace in his hands, tells her the truth—that he bought it for her—and that he loves her. But if she's happy with Chuck, if Chuck loves her as he does, if she can promise him that Chuck will take care of her and never hurt her again, he'll continue to help her find the bracelet and they can both pretend the necklace doesn't exist.
He expects her to nod and tell him she loves Chuck. But Blair shakes her head, moves her hair from around her neck, and turns around.
And Dan fastens the diamond heart around her neck.