As Seen In: "The Collaborators" (Season 6, Episode 3)
And then nothing's the same.
In the third episode of season six, Trudy blacks on Pete after discovering that he's been screwing the neighbor, Brenda. She also reveals that she understood the intent of the NYC apartment from the jump. She was letting Pete play out his masturbatory fantasies because it would all their marriage to continue to be a success from the outside. That's always the perspective that matters in the world of Mad Men.
"I refuse to be a failure," she tells him, and everything you've known about Trudy sharpens. She's always had a handle on business. She's helped Pete get to where he is now, allowed Pete to work her father over for a lucrative account. And it was all a part of the plan to build a successful life in the classic American mode.
Since Pete has fucked that up, she sets some new rules. Now, Pete can only approach their home, her, and their daughter when Trudy gives permission. She's the boss now.