Why?

I look at you now, and I wonder...
What was I thinking?
But I fell so in love with you, it was sickening.
And I don't regret any part of it.
Except the fact that you went behind my back and cheated,
You went begind my back and lied,
And you tore out my heart, along with my trust, my courage, and my confidence.
So in the end, I really did regret it.
I regret every part of it,
But I still look at you wishing I had you back.
Why?