Nobody in this poem is accused of anything dramatic. There is no betrayal scene, no confrontation, no slammed door. What hurts the speaker is smaller and harder to argue with: a former closeness has changed, and a third person seems to bring out a version of the beloved that the speaker never met. Beneath the jealousy is a question the poem can't answer, which is why the speaker was never allowed to see that side of someone they loved.
The construction is plain, and the plainness matters. The poem has no title, only three asterisks, as if it were pulled from the middle of a notebook, and the lowercase lines with almost no punctuation sound like a thought written down before it could be tidied. The refrain "it's killing me slowly" opens three separate passages, and the repetition does the work of a heartbeat or a sore tooth: the pain keeps returning to the same spot. The word "slowly" is the key. Nothing sudden happens here, and the damage comes from watching small changes pile up. The claim is also a hyperbole, and its exaggeration reads as honest, since this is how heartbreak feels from the inside.
Look at how the refrain moves. It begins with "the thought of you and her," which is something imagined, a picture in the speaker's head. By the second stanza the pain has a sound: "the way you laugh / when you never did that in the past." The jealousy now rests on something observed, and the detail is oddly tender. The speaker isn't hurt by a kiss or a message but by a laugh, the most unguarded thing a person does. "In the past" sounds almost like evidence in a hearing, as though the speaker has been quietly keeping a record of the old behaviour and is now comparing it with the new.
The third refrain deepens this into a question of identity: "how your mood changes / when you start talking to her / it's like you become someone else." The simile is the poem's most revealing moment, because it shifts the blame away from the rival and onto the relationship itself. The "her" stays a bare pronoun throughout, with no name, no description and no flaws listed. She matters only as the person in whose company the beloved turns into someone else. If the other person is a stranger, the speaker is left facing an uncomfortable idea: the "someone else" may have been inside the beloved all along, waiting for the right audience.
The last stanza abandons the refrain and the poem's grip loosens. "It was never like that with us / and I can't figure out why" is the most vulnerable line, since the anger turns into self-questioning. There is a small tension with the opening, where "it's not like how we were" implies that something good once existed. The poem seems to mean that the two had closeness, but not this particular ease and joy. Then comes the stray, isolated "maybe," a pause where the speaker gropes for an explanation and settles on fate: the relationship was "doomed / to die."
The ending is the poem's one clear rhyme, "why" with "die," and it lands like a door clicking shut. The line break after "doomed" makes us wait for the verdict, and "to die" is short and final. The verb has also moved. All through the poem the speaker is the one being killed, but at the end it is the relationship that dies, and the speaker takes the role of someone watching. Calling the relationship "doomed" can be read as comfort, because if it was always going to fail, nobody is at fault, neither the speaker nor the laughing beloved. It can also be read as defeat. The poem doesn't say which, and judging by that unsure "maybe," the speaker may not know either.
The poem's significance is its ordinariness. It doesn't dress jealousy up in grand metaphors. It picks out one real, recognisable pain, the discovery that someone you love is more alive with another person, and gives it simple words that anyone who has felt it will understand.