Levin can't cope with his brother's situation at all. It fills him with disgust and helplessness. He's caught between impulses: he can't bear to be in the room with Nicholas, but he also can't bear not to be with his brother
Kitty has an entirely different approach. She considers it her womanly duty to help her brother-in-law, and to this end she sets to work making his life infinitely more comfortable for him. Kitty has the room (and Nicholas) cleaned, calls for a doctor, and visits the pharmacist.
Nicholas begins to call Kitty "Katya," and he sings her praises. She thinks incessantly of what Nicholas might need and can always anticipate his next request.
When Nicholas kisses Levin on the hand, Levin is overcome with tears and must leave the room.