Written in the second person, "Quit" speaks to a "you" who wants to give up but can't, because of one person: "him." The speaker tells this story as if talking to someone they understand well, and the poem suggests that person has been badly hurt. He used their weaknesses and secrets against them for what "seems like years," then left without caring.
What stands out is the strange loyalty at the center. Even after all this, "you" keep staying strong for him and don't want him to feel their pain. The speaker admits this "isn't fair," and that short, blunt line carries a lot of weight. The mood is heavy and tired, but also stubborn. The plain wording and short lines make it feel like someone talking themselves through a hard moment. The final "For him" leaves a bittersweet, uneasy note: this strength is real, but it is aimed at the wrong person.