Give me a promise

Give me a promise
that I could never break
and take from me the freedom to repel
the make-believe I held
to be true,
until you;
had I knew
that sacrifice to save your life
is no price at all for how I'd fall
and fall and fall on every sword
to see you from the blade.
How could I have known to 'die for you'
was not a promise to step before the shot,
but how I could not live if I did not.