Why did I slap you?

Why did I slap you?
I don't know:
May be it was because
You were smiling at my anguish
And agony, and saying falsehoods
To my face.
I was a bit rattled already;
I'd never raise my hand,
I wish and only wish
That you would understand.
I miss you sorely
But you have moved on,
I wish that you had heard
The painful song,
Then playing in my heart;
I want to caress that cheek,
Now I'm so meek,
To forgive myself
Is all I really seek.
You have left me
And for good,
I wish you all the best,
Every moment we encounter
Must verily be a test.
Know that even though you are far,
My eyes see you near,
I wish I hadn't done the unthinkable,
I wish I could quell my fears.