Roberta is obsessed with Betty, but for me, it’s mostly Don (although all of the characters have their fascinations).
What I learned in Episode 12 was that Don is improvising, and he’s operating out of panic. We know a bit about his childhood; “I’m a whore-son” he said matter-of-factly in Episode 8. My thoughts at first was that he had an intense (and justifiable) urge to get away, that he was full of rage, and that he was a social climber. Dick Whitman couldn’t have the home in Ossining, so Dick Whitman had to be over.
But in Nixon vs. Kennedy I saw something different: Terror. Don fears he can be dragged back to “Dick Whitman, Whoreson” at any time. His escape hangs by the thinnest of threads. And all he really wants to do is run. He wants to run with Rachel. He wants to drown in the comfort that Rachel offers, and he wants that comfort to be a running away of a kind.
All of it is improv. He had no master plan when he became Don Draper, no plan when he buried his past, no plan when he didn’t get off the train. It’s all a little boy running away from home with his meager possessions tied in a bundle and resolutely refusing to cry.