I went back to my abusive husband?

I have been cheated on, verbally and physically abused, by my husband of almost two years. I left for a week. I went back to gather evidence of his affairs, but we have been having sex and we seemed to have fallen back into our old routine. I know things will not get better and he will never change and I know there has got to be something wrong with me! I just feel like its my home and I have the right to be there. I know that we are over, so why cant I just leave