Nikky's speaker is stuck in a mind that feels both empty and overcrowded. The opening lines contradict themselves on purpose: the head is "empty" and "full," holding "nothing" and "everything" at once. That tangle is what being overwhelmed feels like, when thoughts arrive all together and none of them can be sorted out.
The middle stanza makes the cause clearer. The speaker wants to move on but can't leave the past behind, because of "the nasty things you did to me that night." The poem doesn't spell out what happened, but it suggests something harmful, and the fear lingers even in ordinary breathing, as if the other person is still there to stop it.
The last lines call it "poetic" that someone who is gone still shapes every thought, breath, and love. The tone sounds bitter and tired. The mood is heavy and haunted, with a painful sense that freedom hasn't arrived yet, even though the person has left.