Thanks for your comments Chuck.

I know it isn't obvious in the 2nd line what's going on but I didn't want to make the whole situation too explicit. I thought it was OK to leave a bit of mystery and imagination there and allow the reader to try to fill in the gaps for him or herself. So long as you get the general impression that the narrator is wondering why the "desert island girl" shows him the scan and coming up with a theory, a bit of ambiguity doesn't matter. Again, I know it isn't obvious why she is a "desert island girl" but if you understand it as a general term of endearment you've got the point.

I hope there were enough clues to tell you that the scan is a pregnancy scan and the hence the "doubly" radiant body is radiant from the woman and her unborn child.

This piece is supposed to be about an unrequited love ("useless" as described in the poem) and the narrator's attempt to come to terms with this ("cauterising the heart") by taking some kind of spiritual comfort from the simple wonder of the woman's pregnancy.

If it needs this much explanation then it hasn't really worked :-(

I'm glad you liked the last stanza. It is deliberately structured so that, that is the only rhyme 'cos I thought it was more powerful to finish on a rhyming couplet.

I suspect the partial explanation for your last comment is that sadness is a better motivator for writing than happiness. A full explanation would say why, but I can't answer than one.