Characters: Luthien, Beren
Book/Source: Silmarillion, Tale of Aragorn and Arwen (LOTR Appendices)
Disclaimer: The word "cleave" memorably occurs in the conversation between Arwen and Aragorn on Cerin Amroth; so here is a re-write of that conversation as adapted for Luthien and Beren.
‘Luthien!’, asked Beren. ‘Do you truly not wish to return to the land of your people and the home of your kin?’
Such things were no longer for him—home and kin lost in the darkness that had consumed Dorthonion—but the more cruelly unnatural did it seem to him that Luthien Tinuviel should lose them, too, and for his sake.
‘I will cleave to you,’ said Luthien, ‘wherever you go, for you are my home and my kin, before all others. Whoever separates us now must needs leave me cloven in twain, the very core of me split asunder.’