Hell if I know. Two pathetic characters in pathetic circumstances in a tiny little nothing of a story. It is only the remarkable work of Cage and Shue that make it worth sitting through Leaving Las Vegas . In Shue's performance we see a woman who wants better, but just doesn't know how to do any better. So she rationalizes up the hilt.
Prostitution is just a job involving sex.
Ben tells Sera he is an alcoholic and he is going to die and that is not going to change. Sera tells him that it's okay. And as the film proceeds she professes, and continues to profess, her love for him. Until he dies. Which is not the sign of a well-developed story.