this isn't a song...it is a concept album.
+1. This could be half an album... I'm afraid to add ideas coz they could be gold.
I have never written / recorded a complete song with lyrics. But I can feel the potential for a pink floyd type flow. Something along the lines of wish you were here...
I gotta listen to that album tomorrow... good luck with the writing. poetry is a finicky think. From some angles perfection looks rubbish or too obvious. Feel the character and try to come up with blank verse and/or a short story. Feel the despair and denial (or whatever you want the song to capture) and go from there.
That could be totally useless but that's where I'd start. I love music with soul. The lyrics are a hard part to get right.