I Am Surprised That...
....with the self-centered, suspicious witch that Anna was and how annoying Kiera Knightly is in just about every role she plays, that Vronsky didn't beat her to the punch and throw himself under the train.He was free to marry, but her flight from her marriage and unashamed flaunting of her broken marriage vows (affairs were tolerated as long as they were conducted discreetly according the the rules of aristocratic society, even though virtuous wives like Dolly and Kitty were the ideal), made her ability to remarry even after the divorce impossible, so she saw his every interaction even with women he had known his entire life with suspicion followed by wild accusations and arguments.
Vronsky loved Anna, and didn't want anyone else, but he did have other interests and responsibilities. She had callously left all of her responsibilities behind and centered her whole life and voracious romantic love around him. That type of love is more a burden than a pleasure.
Anna is an annoying character, and Knightly with that horrible grimace makes her even more annoying.