Manipulation and Wit
And she can't breathe because he's suffocating her. He's drowning her because if he's weak then she better be weaker. And she'll let him because she knows underneath it that entire he loves her. He'll make her grovel at his feet because he knows that he has to at least appear stronger.
And he can't see how much he's hurting her through all the scotch and cigarette smoke. He can't see that she is drowning and suffocating. And she can't see that he's hit rock bottom and that he's falling harder than they both ever thought was possible.
And he can't think straight because he knows that she's killing herself slowly through her own sweet slow suicide. She's throwing fake smiles and kissing up to people. She's purging up blood and smiling through vomit. She's in her own twisted suicide.
And they both know because they're Blair (wit) and Chuck (manipulation). They both know that the audience won't know. All the audience sees is how dear (ditzy) Nathaniel and sweet (drunk) Serena are smiling pretty and twirling their halos of perfection