The speaker is touching a person's body for what turns out to be the last time, and trying to memorise it by hand. The opening line, "my arms feel wrong," hints at the ache of being close to someone you are about to lose. From there the poem moves through the scars one by one: a fall from a tree, a slip on a bench, a fight outside a supermarket. Most are ordinary childhood marks, the kind that come with a story.
Then the list darkens. There are scars the person made themselves, and burn marks from their father's cigarettes. The speaker doesn't flinch or comment. They take in "good and bad" together, which shows how completely they love this person, wounds included.
The mood is tender but heavy with grief. The final line, "it feels like a goodbye, and it was," shifts into past tense, so we realise the speaker is looking back, still holding onto those memories.