The speaker starts with a small admission: something that was meant to be minor has grown far bigger and worse than they ever intended. The poem never says what "it" is, which makes the feeling easier to recognise. We know the sense of a plan unravelling without needing the details.
The weather mirrors that spiral. A gentle breeze turns into a thrashing gale, and the rain starts pelting the ground. The speaker sounds worn down and a little defeated, repeating that nothing goes to plan and that it's safest to expect the worst. The image of a "confused expression sitting upon the ledge" suggests someone frozen and unsure what to do next.
The ending adds a twist. Even after all this chaos, the speaker admits they can't imagine life without "it." The mood is anxious and resigned, but that last line adds a pull of attachment, as though the mess is something they can't bring themselves to let go of.