Factual error: When Julia Roberts takes a photo of Natalie Portman crying she uses a 35mm camera. The final photo in the gallery is from a Hasselblad type camera shooting a square format. All the prints show the full negative and the outside area of the negative. Also when she uses the 35mm camera sometimes she advances the film manually and sometimes you hear a motor drive. It would be either one or the other. Last she doesn't focus the lens when she takes a picture.
Factual error: Jude Law and Natalie Portman are chatting on bus number 109, signed 'Westminster' and driving up Whitehall. Route 109 goes from Brixton to Croydon and nowhere near Westminster, and does not use the old Routemaster bus they are on.
Factual error: When Clive Owen is chatting on the internet to who he thinks is Anna, you can see the URL in web browser. The domain used is "www.nopop." It's impossible for the domain to be missing its top-level suffix (eg. .com).
Answer: I think it was because of the offer that Larry made to Anna. He promised that if they had sex one more time, he would leave her alone and never contact her again. The fact that he was willing to give her freedom, is what made her choose him. Dan was more "needy" and pushy, which is hypocritical, because he left Alice based on her being needy.
Dan left Anna after confronting her about sleeping with Larry for the divorce papers. Anna begged Dan to not stop loving her, to not leave her. Looks like Dan could not stand Anna after she slept with Larry so she went back to Larry since she never turned in the divorce papers.
But after the incident, Dan went to Larry's office and begged him to "let" Anna return to him.