The one with the secrets

Dear Diary,
what's it like to be the locket to her heart?
What's it like to know
all that can't be revealed,
Of true feelings, or of unspoken pain
I know, your lips are sealed.
And I know,
To help her, you did your best,
listening to the truth,
never to judge,
never to criticise,
lending her your ears,
when no one else would.
I want to know what happened,
and like you, try my best to help,
and discover a world that's hers.
But you made a promise,
one that you cannot break,
one that would mean,
even after she moved on,
the pain will still be with you forever...
Yours truly,
for eternity...