Having agreed to everything that Anna wanted, Karenin is left completely alone in Petersburg, and it turns out he's bad at coping.
Karenin had just forgiven and decided to love Anna and her illegitimate child, and now he's abandoned, disgraced and laughed at by society.
For the two days after his wife's departure, Karenin goes about his business as usual and suppresses all his despair.
He falls apart after a clerk from a fashion house comes to settle an unpaid bill for some of Anna's clothes. He can't bear the contempt he sees on everyone's face.
What makes matters worse is that Karenin has no friends, no one to talk with about his situation.
Karenin has no family, and all through his studies and career, he never formed any close friendships. He has people to network with, but no people he can really trust.
Karenin thinks about his early life with Anna. When he had achieved the post of Governor, Anna's aunt introduced the two of them. It got to the point where Karenin felt it was inevitable to propose to Anna, and after much debate, he finally did.
Karenin's closest relationships are entirely official in nature and never touch the personal sphere.
As for his female friends (the most important of whom is Countess Lydia Ivanovna, whom we met in Part 1, Chapter 31), Karenin doesn't even think of them. All women intimidate him on some level.