Ben Sanderson (Cage) is a Hollywood screenwriter whose alcoholism costs him his job, family, and friends. With nothing left to live for, he heads to Las Vegas to drink himself to death. As he drives drunkenly down the Las Vegas Strip, he nearly hits a woman, Sera (Shue), on the crosswalk. Sera chastises him and walks away. Sera is a prostitute working for an abusive pimp, Yuri Butso (Julian Sands), a Latvian immigrant. Polish mobsters are after Yuri, so he breaks his relationship with Sera in fear that the Poles may hurt her. Yuri is murdered (off-screen) shortly afterwards.
On his second day in Las Vegas, Ben goes looking for Sera, introduces himself and offers her $500 to come to his room for an hour. Sera agrees but Ben does not want sex. Instead, they only talk and form a bizarre romantic relationship and Sera invites to Ben to move into her apartment. Ben instructs Sera never to ask him to stop drinking. Sera asks Ben not to criticize her occupation. At first the two are happy, as Ben is "totally at ease with this (Sera's prostitution)." However, each becomes frustrated with the other's behavior. Sera begs Ben to see a doctor which makes him furious. While Sera is out working Ben goes to a casino and returns with another prostitute (Mariska Hargitay). Sera returns to find them in her bed and throws Ben out. Shortly afterward Sera is approached by three college students at the Excalibur hotel and casino. She initially rejects their offer by stating that she only "dates" one at a time, but eventually acquiesces when she is offered an increased price. When she enters their hotel room, the college students change the deal and request anal sex, which Sera refuses. When she attempts to leave, she is brutally attacked and raped. The next morning, she is spotted by her landlady returning home battered and is evicted. Sera receives a call from Ben, who is on his deathbed. Sera visits Ben, and the two make love. He dies shortly thereafter. In the final scene, Sera explains to her therapist that she accepted Ben for who he was and loved him.

Question: Why was the Sanderson kicked out of the prostitute's apartment?
Answer: Ben brought another prostitute back to Sera's apartment
Alternative answer: He was with a different prostitute in Sera's bed.