Thank you for sharing this poem with us! I'm wasn't too clear on the circumstance or setting of the poem, but I gleaned the following. My thoughts were that it was about a moment after being married where a spoken word has profound potentially painful results.

'no beginning / no end,' and "a single word
has the power
to melt or cut two hearts!"

when coupled with the unhappily ever after, i think of something like, Divorce, cheating, or betrayal. My question is, "WHAT IS THE WORD?!"

I think it is great that the speaker doesn't tell it. By omitting that word it makes me come up with my own reasons. what would make me melt, or will overpower even true love? is the word 'death?'

well done!