Her own people are the worst, as evidenced by everything about her, so it would be wrong for Andrei to send her there. Here at least she'll have the salutary moral influence of his dad and sister, and won't have any fun be surrounded by friends the baleful influence of people who actually seem to like her shallow Petersburg society.

The thing is, she's genuinely, justifiably terrified of giving birth, but he thinks she's still coquetting, or at least is determined to pretend he does. He's been disappointed in her and it's completely cut him off from sympathy; he's like Nora at the end of The Dollhouse, horrified to have been sleeping with a stranger all this time. And she has no idea what she did wrong (I'm not sure even Andrei knows) and he's just given up completely and forever on trying to explain or confide in her about anything.

WELCOME TO TOLSTOY.