[Nerwen]

I think the speaker is your namesake, Urwen/Lalaith, and the one addressed is Fëanor.


Fire you were named for
And, originally, so was I -"Spirit of fire" and "Fire-maiden"
Renowned you were, and I was not
And death was what we got -I don't think this needs elaboration.

The vast lands of Beleriand
Neither of us got to see -Neither Dor-lómin, where Lalaith lived out her short life, nor Mithrim, where Fëanor died, are part of Beleriand proper.
I was too weak to live
You were too fey to wait or flee -She died from a childhood illness; he was killed in battle due to his recklessness.