Empty

Why is it that a person finds themselves trying to prove something to another? Not in a competitive sense, but a inner longing to do so.
As a child my dad was absent quite a bit,whether it be an affair,drinking, work or what not. I remember finding myself often scared to death when he would go on his alcohol rages, which lead to added stress on my mom. I soon came to know the evil things a parent can say. : I should have had an abortion," "it's your fault your dad's gone," " we never wanted you," should I go on? I grew up wit this empty hole inside that has never been filled. My grandparents were the only ones I had that were stable and yet I still have the empty feeling.
My mom has now found God, remarried and for the most part has done a 360. On the other hand, my dad found his wife (affair) and decided to have kids and adopt more. The constant rubbing in your face about the things they buy for them or the time they spend on expensive vacations are enough to kill someone who longed just to know her daddy. I put up a false front, a smile that hides the crushing of my heart. I've never asked for anything materialistic from my daddy. Just love. The kind of love that I've seen other daddy's and daughters share.
Now I find myself always dropping whatever I'm doing to help him and his family but in return.. not even a thank you, almost like it's expected of me. I still have that empty feeling. It never goes away. I get the comment quite often asking why am I trying to prove myself to him. I step back look at the events and answer every time......because he's my daddy.