Lyric discussion by istolethejerseys 

Appears to me that the thorn is his conscious (or possibly an allusion to Paul's, with the relationship being the source of the pain as opposed to Paul's side). Could be about him experiencing anguish after being with some girl (cringing in her bed) in what he retrospectively sees as a futile attempt to feel connected. He feels guilty about using her, making her breath incendiary and her presence a burden. In stead of changing his ways based on how he feels he continues to be with this girl (laying infected with the thorn as opposed to tending to it in the last line)

i agree with dominicolas, i think its about a purely sexual relationship, and he cant feel anything past that for her.

haha that wasnt meant to be a reply. my bad

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