How we cite our quotes:
Levin did not care to eat, and he was not smoking; he did not want to join his own friends, that is Sergey Ivanovitch, Stepan Arkadyevitch, Sviazhsky and the rest, because Vronsky in his equerry's uniform was standing with them in eager conversation. Levin had seen him already at the meeting on the previous day, and he had studiously avoided him, not caring to greet him. He went to the window and sat down, scanning the groups, and listening to what was being said around him. He felt depressed, especially because everyone else was, as he saw, eager, anxious, and interested, and he alone, with an old, toothless little man with mumbling lips wearing a naval uniform, sitting beside him, had no interest in it and nothing to do. (6.29.2)
Levin is practically the only one who doesn't have a strong interest in how the elections are proceeding; this is yet another way he sets himself apart from the social norm.
"What does he keep reading philosophy of some sort for all this year?" she wondered. "If it's all written in those books, he can understand them. If it's all wrong, why does he read them? He says himself that he would like to believe. Then why is it he doesn't believe? Surely from his thinking so much? And he thinks so much from being solitary. He's always alone, alone. He can't talk about it all to us. I fancy he'll be glad of these visitors, especially Katavasov. He likes discussions with them," she thought, and passed instantly to the consideration of where it would be more convenient to put Katavasov, to sleep alone or to share Sergey Ivanovitch's room. (8.7.6)
Kitty instinctively understands that her husband's preoccupation with philosophy is not helping resolve his existential dilemma. She fears that he's not learning anything by isolating himself from other people.
"No, I'd better not speak of it," he thought, when she had gone in before him. "It is a secret for me alone, of vital importance for me, and not to be put into words. (8.19.13)
When Levin finally achieves spiritual peace, he consciously makes the decision to keep his happiness to himself and not to share it with his wife. Check out Levin's "Character Analysis" for more on Levin's personal epiphany.