The intoxication of the news that Kitty was not married had gradually begun to work upon him.

Kitty was not married, but ill, and ill from love for a man who had slighted her.

This slight, as it were, rebounded upon him.

Vronsky had slighted her, and she had slighted him, Levin.

Consequently Vronsky had the right to despise Levin, and therefore he was his enemy.