Deception of the heart

We were swaying to the music.
The guitar was very acoustic.
My slick dark green dress hiding my dagger that is white,
As I wait for the right time to use it in the cover of the night.
I was given a task to kill you but I must start with a disguise.
In our time together, I have fallen for you, and that's partly why I truly feel sorry for the lies.
I hope you know that I will miss you dearly,
But I must forget you to continue my work clearly.
At this very moment, I stabbed you in the heart
And walked out knowing that I had to depart.
I won the final round
And now I am the one that is to be crowned.