The speaker is stunned by one night with another person, when the defenses they've spent years building suddenly fell away. The opening is raw and almost breathless, a string of angry-sounding questions that are really amazement: why did their hands fit, why was breathing suddenly so easy? The line break on "every / single / fucking / one / of / them" makes the collapse feel slow and total.
The central image is a garden turned fortress. The speaker describes stone walls, fences, and poison ivy vines that people used to get under their skin, and says they planted themselves in the ground at eight years old and haven't moved since. The poem hints that something went wrong in childhood, though it never says what. With this person, the speaker pushes the vines aside, looks out, and sees only them. The mood is relief mixed with disbelief, and the ending, feeling "free for just a night," carries a quiet ache that it may not last.