Why do you hurt me?

Who knew one person could change my mood so drastically?
Who knew you could make go from extremely happy to in tears,
Within seconds?
Or vice versa.

You speak to me when you choose.
You speak to me when you need something.
You speak to me because I'm the only person,
That will stand by you through think and thin.

You have a girlfriend now,
So why are you here?
Causing more pain than good.
But then I can't let you go.

I told you I'd always be here.
But it's killing me to stay,
And it's killing me to go.
Either way I am dying.

You open up and break my heart,
Shatter it to tiny pieces.
I open up and let you know why,
You read it and don't reply.