The Hunger Games

As punishment for a past rebellion, each of the twelve districts of the nation of Panem is forced by the victorious Capitol to annually select two tributes, one boy and one girl between the ages of 12 and 18, to fight to death in the Hunger Games. In District 12, Katniss Everdeen volunteers after her younger sister Primrose is initially chosen by lot. She and the male tribute, Peeta Mellark, are escorted to the Capitol by chaperone Effie Trinket and their mentor Haymitch Abernathy, a past District 12 victor and alcoholic. Haymitch impresses on them the importance of gaining sponsors, as they can provide gifts of food and supplies during the Games. During part of a series of televised interviews, Peeta publicly expresses his love for Katniss, which she initially takes as an attempt to earn sponsors for himself but later learns that it could help her. While training, Katniss observes the Careers: Marvel, Glimmer, Cato, and Clove, tributes from Districts 1 and 2 who have been training for the Games from a young age.
At the start of the Games, Katniss ignores Haymitch's advice and grabs supplies from the ground around the Cornucopia, a place filled with food, weapons and other supplies where the contestants start, and narrowly escapes being killed by Clove; about a quarter of the tributes are killed in the initial melee, and only eleven survive the first day. Katniss tries to stay as far away from the other competitors as possible, but Head Gamemaker Seneca Crane triggers a forest fire to drive her back towards the others. She runs into the Careers, with whom Peeta has seemingly allied, and flees up a tree. The Career pack fails to kill her and Peeta advises them to wait for her to come down.
She notices Rue, District 11's young female tribute, hiding in an adjacent tree. Rue silently draws her attention to a nest of poisonous tracker jackers, genetically modified wasps that can cause hallucinations and death. Using a serrated knife, she cuts the branch holding the wasps, causing it to fall and release them onto the Careers. Marvel, Cato and Clove escape, while Glimmer succumbs to the venom and dies. Katniss is stung, and becomes disoriented from the venom, hallucinating the death of her father. After Rue helps Katniss recover from the poison, they become friends. Katniss devises a plan to destroy the cache of supplies that the Careers have been hoarding. After Katniss succeeds, Cato angrily kills a boy from District 3 who was supposed to be watching the supplies. Marvel finds them and kills Rue with a spear, and Katniss shoots him in the heart with an arrow, killing him. Katniss comforts Rue with a song; after the girl dies, the grieving Katniss places flowers around her body. She then holds three fingers up to a camera, as a way to honor Rue towards District 11 and to show a symbol of disgust towards the Capitol. The people of District 11 watch and then riot, leading President Snow to warn Crane that these Games are not turning out well.
Haymitch persuades Crane to change the rules to allow two winners if they are from the same district, suggesting that this will quiet the unrest. When this change is announced, Katniss searches for Peeta, finding him wounded after fleeing from the Careers. He tells her Cato found out that he was intending to return to Katniss, leading him to stab Peeta with a sword. After she moves him to safety, they hear an announcement that what each survivor needs the most will be provided at the Cornucopia. Despite Peeta's strong opposition, Katniss leaves to get medicine for him. Clove attacks and pins her down; she then boasts about her part in Rue's death. Katniss is saved when Thresh, District 11's male tribute, kills Clove. He spares Katniss's lifeÂ â onceÂ â for Rue's sake. The medicine heals Peeta.
The two devise a plan to leave fatal Nightlock berries out for Cato so they can kill him, but Peeta disappears and Katniss is horrified to find the berries on his jacket. Peeta is found fine, and they discover District 5's female tribute whom Katniss had dubbed "Foxface" (due to her appearance and agile nature which allowed her to escape the wrath of the Careers) dead after consuming the fruit. For the finale of the Games, Crane has wild beasts unleashed into the arena which attack and kill Thresh. The beasts chase Katniss and Peeta onto the roof of the Cornucopia where Cato is hiding, and after a long fight, the two subdue him and throw him to the beasts below, which maul him. Katniss then proceeds to shoot and kill Cato, ending his misery.
Katniss and Peeta think they have won, but Crane cancels the rule change: there can be only one victor. Katniss then convinces Peeta to eat Nightlock berries with her. Just before they do, they are hastily named co-winners of the 74th Hunger Games.
Afterward, Haymitch warns Katniss that she has made many enemies by her acts of defiance. Snow has Crane locked in a room where the only source of food is nightlock. As Katniss and Peeta return to District 12, Snow ponders the situation. Katniss encourages Peeta to forget what happened between them in the Games, devastating him.

Question: Why does Katniss leave Peeta?
Answer: Get medicine