Chuck is now, remember, implicated in the Bree/Carter thing and 1) on Bree's side, 2) thus on Nate's side, 3) therefore on the side of the Good Guys because Carter is bad, 4) while also screwing Carter over, and 5) still confused about Blair's whole deal w/r/t both of them. Oh, and 6) Blair doesn't know that her new/old trust in Carter is still misplaced, he thinks, which means he's also protecting her from getting hurt both personally and via her love of his sister, who is 7) also in need of protecting, which always makes him twice as scary and sneaky. So in fact all three people most likely to make Chuck act totally insane and get totally destructive are in, as far as he knows, real danger from a guy he already hates. Wow. I really didn't think Blair and Chuck had a lot to do in this episode, but I thought wrong. This is totally fascinating.
And it's even more perfectly balanced than that, because Chuck and Blair are both working the same angle, which is the only angle they ever work, which is that the only constructive thing they bring to the group is the power of exclusion: They're always the watchdogs, while Nate and Serena are always the inviters-in. They bark and bite, which allows Serena and Nate to be who they are, which is the only people on this entire show that ever allow themselves to feel actual feelings and are constantly fucked by that. They are the immune system; they spent the last two years keeping Vanessa and Dan, among others, standing at the door until they could smell them enough to make sure. So this time, the only reason they're at cross-purposes -- very subtle -- actually is the fallout from their relationship: Blair wants Carter to be an okay person because that means Chuck is an okay person; Chuck wants Nate happy with Bree because that means the chapter is really over, and on a minor note -- not huge, we've dispensed with the Jules et Jim of it all, except for how it seems to, appears to, be a sudden issue today -- it's okay to keep loving Blair.
Anyway, Chuck is doing some kind of crazy manipulation on top of Blair that causes her to moan her way through an entire monograph about how Carter is not the bad guy anymore, and sorry to mention it but he wasn't the cause of her first Yale spiral, just a very good symptom of it, and plus he makes Serena happy. At that point her eyes cross in pleasure, and Chuck explains that he's doing buntautuk on her, which he learned from a master in Chiang Mai during his pre-Jack trip to Thailand. And here we thought it was just heroin and whores. "Serena's deluded," Chuck explains. "The guy's not capable of genuine feelings." Blair's not buying it; Blair's not really talking about Carter: "He's brought out a different side of her. They're all happy and domestic."