I hit my girlfriend ?

Today I pushed my girlfriend and hit her. I am so ashamed. This is not the first time I've done this, but I want it to be the last. I don't want to lose her emotionally and/or physically. We often bicker amongst one another, but in sort of a playful type of way, and it can often times lead into arguments. I often times say that it is she who starts the arguments, and iI really do feel that way. I hate arguing unless there is really some meaning to the situation. We argue and she will do things that she knows will anger me and in an instant I explode. I hit her and I feel awful as soon as I've realized what i've done it hurts me to see what I have done, I feel disgusted and ashamed. So it switches from her as the aggressor to me and then in the end I'm the bad one. I really don't consider my self an abuser, because I just don't come home and start hitting on her because dinners not ready, I dont black her eye , but i have gotten really rough. It dosen't happen often but it has more than once. I need and want help.