Abbie's poem is about the helpless, stubborn feeling of missing another person. The speaker says there is no "right or left" to it, meaning there's no correct direction, no proper way to go about it. It also doesn't wait for a good moment. It arrives whenever and wherever it likes, and all you can do is "just do it."
The speaker sounds a little worn out and a little defiant. The line "You can't control it. Or anything" slips from one feeling to a much bigger sense of powerlessness, as if missing someone makes the whole world feel out of hand. Then "I swear" adds a rough, honest edge, like someone insisting on something nobody has quite believed.
The repeated line "missing is missing" opens and closes the poem. It works like a shrug and a statement of fact at once: this feeling can't be explained or fixed, only named. The mood is quiet, raw, and plainspoken, and the simple wording makes it feel true.