Gaara became nihilistic and murderous after his uncle lied to him about his mother hating him and learning that his father put shikaku in him and tried killing him several times. Naruto compared to Gaara because they were both Jinchurikis and pariahs in their village. Naruto defeated him, spared his life and made him open his eyes to how friendship beats being alone. In this sense, Naruto was the first person to not fear Gaara and acknowledge him, thus he regarded him as his first friend. Naruto later risked his life to save him again.
Following Naruto's example, Gaara was able to reform his village, get acknowledged by the people and become Kazekage.
