Written in short, plain lines, the poem moves from despair to a small, fragile hope. The speaker opens by admitting a feeling of wanting to give up, as if nothing is left. Then comes the turn, marked by the single word "But." One person changes the picture. He makes the speaker feel better about herself and can even bring a smile when she is angry enough to "tear someone's head apart."
The most telling detail is that he has no idea. The speaker keeps her happiness to herself, which suggests a quiet, maybe unspoken affection, or at least a gap between what she feels and what she says.
The ending pulls back toward the heaviness of the start. "Sometimes I want to run away / But I can't." It's unclear whether something is holding her in place or whether this person is the reason. The mood is raw and honest, hopeful but unsettled, with the good feeling never fully winning out.