Seven short lines, one unfinished sentence, and a small trap that closes on the reader. On the surface the speaker is complaining: all those nights spent thinking of "you" might have gone to "a million / Other things." But look at the first line. "Thinking about" is happening now. The poem is itself one of those nights. The speaker laments time lost to this person while spending more of it on them, so the complaint turns into a confession. That is the central idea: regret about an obsession can be the obsession's most faithful form.
The grammar carries much of this. The poem has no finite verb in its main clause. It never says "I think" or "I am thinking," only the bare participle "Thinking," which has no subject and no beginning. The thought seems to have been running before the poem started, and nothing marks where it stops. The full stop after "you" is the only punctuation, and it arrives like a door shutting on a thought that has not really ended.
The word "thinking" appears twice, in the first line and again in the fourth, "Spent thinking." This is the poem's loop. The speaker begins by thinking and, three lines later, is still thinking, just inside a hypothetical. Even the imagined alternative, nights spent on other things, is described with the same verb, as if the mind can only be pictured doing the activity it is trying to escape. The sounds reinforce it. "Thinking," "things" and "than" all share a soft, breathy *th*, which gives the poem something like the sound of a sigh. There is no rhyme to resolve anything. The lines don't close with a click, they trail off.
The line breaks control the pace. Most lines are only two or three syllables, so the reader is forced to read slowly, almost one beat at a time. "I could've" is a good example. The line ends on a modal verb with nothing to complete it, and the reader hangs for a moment before "Spent thinking" arrives. That contraction matters too. "Could've" is casual, spoken, a little tired, closer to a muttered aside than a formal declaration. It also holds the poem's tone in suspense. "Could have" spent the nights differently might mean "I wish I had" or "I should have" or even "I was free to, and chose not to." The poem doesn't say which, and the ambiguity lets resentment, regret and tenderness all stay possible.
The imagery is almost entirely abstract, and the few concrete words are carefully chosen. "Nights" is the only setting. Night is when distraction falls away and the mind runs unsupervised, and the plural suggests this has happened repeatedly, not once. Against that, "a million / Other things" is pure hyperbole, a huge but blurry number attached to the vaguest word in English, "things." The poem never names one of them: no books, no sleep, no other people. That vagueness is the point. The alternatives have no detail because they have no pull. Only the single, specific "you" does.
That contrast of scale organizes the whole poem. The lines swell toward abundance, "a million," "other things," and then collapse onto one syllable at the very end. "Than you" is the shortest line, and "you" is the last word, so everything in the poem exists to delay and then deliver it. The grammar of comparison adds a sting: the person is listed as one of the "things," measured against a million rivals. The words seem to belittle "you," yet the structure makes "you" outweigh everything else.
Part of what makes the poem memorable is how much it does without ornament. There is no metaphor, no rhyme, no elaborate scene, and the speaker never says what happened between them and "you," or whether the person is still present. The poem trusts the reader to fill that silence. Its significance lies in this economy: it catches a very ordinary emotion, being unable to stop thinking of someone, and shows it from the inside by making the form do the thinking. Its bare ending also invites the reader to recognize something. By the time the final "you" lands, it can feel as if it was addressed to someone else we have each thought about too long.