"My mom hosted this big party. It was supposed to be about our new family." Dan's actually looking at her, listening to what she's saying instead of gearing up his response. It's kind of weird but very welcome. "But it turns out, of course, it was for publicity. So I blew up at her in front of everyone. And this whole time, I was thinking that Bart was the problem, but I realized it's all her." Dan, proving his active listening skills, offers a fairly facile diagnosis: "You ever think that your mom acts like she's perfect because she's... Too ashamed to acknowledge how far from it she's really been?"
(Or it would be facile, if he weren't really talking about himself. And that's how they got me, because damn. Not to mention he just explained Blair in about the plainest language imaginable, and thus this entire show, Vanessa's whole trip, the greater UES culture, Nate's pride issues... I mean, the show is about the surveillance culture, the way they all, and we, have to be constantly on guard about their propaganda, embodied by GG, and how many ways that can break on you, while you're still trying to remain privately human. How being looked at means being responsible to the people looking at us, and how incredibly difficult and painful it is to retain your grip on anything real when every occasion is an occasion to be false, because it's drastically easier.
It doesn't matter if you're really perfect as long as everybody thinks you are; it doesn't matter if you're really happy, or a family, or good, as long as nobody sees the cracks. But what none of them can imagine -- and it is difficult -- even just one person, somewhere in a secret place, that would look you're your eyes and say they see the cracks and still don't care. That's the home they're all trying to create, for themselves and for each other, all the time -- that's all Dan is about, really; that's all Blair was saying when she said everybody knew how bad it was -- but it also comes back to this: being abject, dancing in freefall, is good. Those are the free places. But they're still not as good as owning the spot where you stand.)
She looks at him, understanding what he means, all the things he means, and apologizes. But just like Chuck and Blair, it's less that she's apologizing first and more just establishing the playing field so that he can apologize without worrying she's going to attack from an unexpected direction. He's very sad, realizing what he lost, and says he's sorry too. And it is so, so great, because all it would take to make Dan bearable is for him to acknowledge what a horrible little trap he helped Serena set for herself, which I think maybe he just did.