Someone has left, and the speaker can't stop waiting for them to come back. The poem is built from three short stanzas, each starting with "Every time," which suggests how often this happens. A car engine, a squeaking door, a phone notification: ordinary sounds and small alerts that most people would ignore become, for the speaker, possible signs of the ex returning.
The last line of each stanza is identical: "Coming to say you want me back." That repetition makes the hope feel stuck on a loop, as if the speaker's mind keeps going to the same place no matter what. Notice, too, that the hope shifts from the street, to the workplace, to the phone, so there's nowhere the speaker can escape it.
The mood is quiet, sad, and a little painful. Nothing dramatic happens, and the poem never says the hope is answered. The plain language and simple structure make the longing feel honest and raw, like a private admission rather than a performance.