Blair was to blame for Elizabeth's betrayal and practically her existence, which caused Chuck to betray her in turn, which caused her to freeze him out, which caused him to fuck Jenny Humphrey, which caused her to lose her goddamn mind and caused him to turn into the crippled Henry and nearly vanish altogether. But because she doesn't have proof that these two things are actually connected, and doesn't really care about anything but -- as usual -- rewriting the narrative the way she thinks it's supposed to go and somehow erasing her past mistakes with the latest iteration, it's all adding up to a crazy conspiracy that isn't being run by anybody. She's always been the immune system of the UES; the one time she didn't hold up her end, it nearly killed them both. When you've got that much scaffolding and that many layers of justification built into your story, the fact of simple jealousy is less implicit than it is irrelevant. Sure, she's jealous. But that's on a list of fifty things and at best it's #35, so who cares?
Dan gets cheesy horny guy again with Serena, this time relating to the ridiculous dress, and Serena for the third time tosses the heavily coded "let's talk about things" thing around, and Dan's like, "Oh I got some things to 'tell' you, too," and it's fairly adorable but suddenly Vanessa's standing there, looking as usual like she's been sucking on free-market lemons, and pointing out in her angriest whiskey voice just how fucking adorable it all is.
Nate yells at Juliet for awhile about Ben and how he, Nate, has never been to her apartment, and that Juliet is hard to make plans with, and it all comes out in a garbled rush that basically comes down to Nate feeling once again like the other woman. Juliet swears Ben's not her boyfriend, but before she can explain that obviously he is her jailbird brother, Nate's off in a huff. "You hate Serena so much because you're exactly like her!" he yells, which is the kind of insult Nate always throws around but is also the kind of insult only Nate really understands. Given that Serena's only romantic flaw is giving each of her relationships exactly the respect and attention they deserve and no more, isn't he really just giving Juliet the upper hand again
Dan's only defense about lying to V is that he had fun for the first time since they moved in with each other. Which isn't an explanation so much as a total burn. But Vanessa does that thing where her naked vulnerability proves the point more than making you want to barf, and is in fact one of the smartest and most complex thoughts any of these people have ever had, all in one breath, starting from first principles and then extrapolating backwards until you can really see what a nightmare coming true this actually is, for her: