Spun

Ross (Jason Schwartzman) is a customer of Spider Mike (John Leguizamo), a methamphetamine dealer. Spider Mike and his girlfriend Cookie (Mena Suvari) are constantly arguing, and Ross strikes up a friendship with Nikki (Brittany Murphy), a fellow addict. Nikki takes Ross to meet her boyfriend, "The Cook" (Mickey Rourke), who supplies Spider Mike with drugs from a meth lab he has set up in a motel room. The Cook gives a small amount of meth to Ross in exchange for bringing Nikki home, and says that he will get in touch with Ross if he needs a driver.
Back at his apartment, Ross gets messages from his mother and his former girlfriend, Amy, wishing him a happy birthday. Ross, assuming that Amy still loves him, sporadically calls her and leaves messages on her answering machine. He then goes to the local strip club while high, leading to an intense pornographic hallucination. He takes April (Chloe Hunter), one of the dancers he has a relationship with, home and has sex with her in a variety of positions, the last of which leaves her tied to the bed naked. As they finish, the Cook calls with an emergency regarding Nikki's dog, Taco, which needs to be taken to the veterinarian. April tells him to untie her but Ross, still high, duct-tapes April's eyes and mouth shut to keep her quiet and leaves her handcuffed to the bed, playing music to cover her gagged screams. Elsewhere, two policemen (Peter Stormare and Alexis Arquette) working with a TV crew raid the trailer where Frisbee (Patrick Fugit), another one of Spider Mike's customers, lives, falsely believing that a meth lab is located there. They take Frisbee and his overweight mother into custody, where they threaten him into cooperation in a drug bust.
After driving the Cook around town to buy ephedrine pills, beer, and pornography, Ross returns to his apartment to apologize to April. In the Cook's motel room, he and Nikki have a fight after a prostitute arrives in response to the Cook's inviting her around. Nikki ends their relationship, and calls Ross and asks him to take her to a bus station so she can go back to Las Vegas, which Ross does, leaving April still tied to the bed. While Ross and Nikki are out, Frisbee is coerced by the cops to wear a wire and buy some meth from Spider Mike so that they can arrest him. When he enters, Cookie attempts to seduce him, as revenge for Spider Mike using a phone sex line. After Cookie finds a wire and the cops bust in, Spider Mike, furious at Frisbee's betrayal, shoots him in the testicles; Spider Mike and Cookie are both arrested. After Ross and Nikki go back to his apartment and find April gone (rescued by his lesbian neighbor (Deborah Harry)), Ross finally drops Nikki off at the bus station, where they share a kiss, and hope to reunite if he ever goes to Vegas.
Meanwhile, the Cook's meth lab catches fire and destroys the motel room, forcing him to return to the adult film store, where he is arrested after the owner calls the police. Once the Cook makes bail, he calls Ross asking for a ride to another dealer's house in the city, which Ross agrees to do so that he can see Amy, who also lives in the city. The dealer provides the Cook with cash, some meth, and the equipment to start a new lab. The Cook promises Ross six months' worth of meth in exchange for being his chauffeur; he agrees on the condition that he can see Amy first. Amy, who has gotten her life together, wants no part of him after seeing that he still uses drugs and can only give her $100 of the $450 he owes her. As the Cook drives a depressed and sleeping Ross back, he talks about how, as a child, he witnessed his mother killing several puppies he could not care for. As Ross naps in his car, the Cook starts up a new lab in an old trailer, but blows it and himself up in the process.

Question: Who is Ross' former girlfriend?
Answer: Amy