I have to say I like this a lot. There are plenty of tales of tragic love out there but this seems more human simply because it's not all doom and gloom. Lines like
"Sing on I shall, though my songs wither, "
sound like vague acceptance of his situation instead of screaming, 'Oh, I die of a broken heart'.
If there's one thing I'd have to make a point of it's that the poem structure itself seems very disjointed and manic and this really doesn't reflect the quiet depression the words portray. Maybe something smoother would have worked better though the loose and occasional rhymes do present that feeling of being slightly numb and confused after said events which I enjoyed.
Only other thing I can think of is that you should either make the langauge completely dated or modern but not jumping between the two. What I mean by this is highlighted in:
O then my Lord, do you feel the pain too?
Twilight it is, for the children of the sky
Seems a bit odd... try changing the first line or replacing it is with 'tis, the genre seems a little bastardised.
Of course, s'just my opinion but I hope it helps
