The speaker visits someone's home and, while there, sees a glimpse of the life that might have been. The person lives there with their children, and the speaker senses a different future, one where the two of them might have shared this kind of life. The poem doesn't say exactly who "you" is, but the tone suggests a past relationship or a missed connection.
The word "hauntology" is the key. It points to the idea of being haunted not by the past, but by futures that never arrived. The speaker feels that ghost in the room. The broken, unfinished lines, especially the repeated "if only," make the thought trail off, as if the speaker can't bring themselves to finish it. The final lines, "what we really wanted," land quietly and painfully. The mood is wistful and regretful, with a sadness that feels private and restrained rather than angry. The speaker accepts the mistakes but still aches over what was lost.