Dog days are over

If could let you in, I would.
There's no real reason not to.
But you're running through my head,
in every directions.
That's something I can't stop.
My heart beats faster when you smile.
Your smile says more than mine ever will.

But while you're hear, I'd like to say what I never would.
You make me feel as if what I believed in doesn't exist.
But what I believed in was not you.
Try to figure that one out, because I can't.