The speaker is trying to quit smoking, and the poem reads like a running list of the thoughts that crowd in on a hard night. Each line begins "Sometimes I wish," but the wishes keep circling back to the same two pulls: the longing for "one, just one" cigarette, and the refrain that "the addiction wouldn't lie to me." Small details, like a sore back after the drive to Hamilton and waiting for Tessa, make the craving feel tied to an ordinary, tiring evening.
The speaker also seems to be part of an online group of people quitting, and feels the weight of staying strong for them while struggling too. Even the advice they give others, that one cigarette is fine, sounds like something they'd like to believe themselves. Christmas adds a wistful note, with the wish to be a child again.
The ending is the most telling part. "Only sometimes" shrinks into "Sometimes ... Often ... Always ...", admitting the struggle is constant. The mood is tired, honest, and quietly raw.