Two lines are enough here for a small drama in two acts. In the first, the speaker thinks of someone and the pain "never seems to subside." In the second, one word, "Until," turns everything around: the hurt eases only when the speaker remembers "what you did to me and why I had to say goodbye." The central idea is a paradox. Thinking about the person causes the ache, but thinking about the harm they caused is the only thing that quiets it. The poem suggests that sometimes we don't heal by softening our memories. We heal by sharpening them.
The title word does a lot of quiet work. To "subside" is what floodwater does when it drains away, or a fever when it breaks, or a swelling when it goes down. The poem never describes any of these, and its only noun for the feeling is the bare, abstract "pain." Yet the verb carries a physical picture of something that rises and refuses to recede. The hedge in "never seems" is also worth noticing. The speaker doesn't say the pain never subsides, only that it seems not to. That small softness lets in a doubt: perhaps the feeling is partly a trick of the mind, and perhaps the speaker already knows the remedy.
The construction is tight. Both lines are built around the same phrase, "I think of," and a single change of object reverses the outcome. "When I think of you" leads to pain. "Until I think of what you did" leads to relief. The speaker's thoughts are the same act pointed at two different targets, one the person and the other the person's behaviour. The dash after "subside" works like a held breath or a sentence swerving mid-stride, and the blank line that follows adds to the pause before the correction arrives.
The grammar shifts power as well. In the first line the pain is the subject of the main clause, and the speaker only thinks, helplessly. In the second, "I" takes charge: "I had to say goodbye." Even there, though, "had to" is not the language of free choice. It suggests a decision made under pressure, one that may still need defending. Judging by the wording, the speaker may need to keep reminding themselves of the reasons, as if longing can make them slip away.
Rhythm and sound deepen this. There is no regular metre, and the voice sounds like speech, even like a confession. The first line is short and almost even, about thirteen syllables. The second runs to about eighteen and spills forward as if the justifications are pouring out. The two lines are tied together by a slant rhyme, "subside" and "goodbye," which share the same long vowel but not the final consonant. They nearly click together without quite doing so, and that suits a poem about a farewell that does not fully resolve. That long "i" sound also echoes through the second line in "I," "why," and "I" again, so the sound of the speaker's own pronoun runs through the explanation. In effect, the speaker is claiming the story as their own.
What the poem leaves out matters just as much. We are never told what the person did. "To me" marks the speaker as the injured party but gives no details, so the reader fills the gap with their own experience. That openness lets a two-line poem hold a great many separate stories, and it keeps the focus on the speaker's reaction rather than on the offence itself. A reader might also smile at the signature, "Sherlock," and see something of a detective's method in the way the speaker reasons backward from the evidence of the wrong to the necessity of the parting. That is only a reader's fancy, though, and nothing in the text depends on it.
The poem is dated August 28th, 2015, and that date, along with the name and the title, is all the information that comes with it. It does not need more. Its significance lies in its honesty about a mixed feeling that many people know and few admit. The relief it offers is not peace, because one painful thought is traded for another. The poem ends on "goodbye," the very word that began the loss, and it leaves us wondering how long the cure will hold before the speaker has to remind themselves again.