Domestic Abuse: How to get Out

When in a abusive relationship,who is really at fault- the man, woman, or both? Why do the victim make excuses for the aggressor abusive behavior? (ie: he's stressed at his job, he had a little too much to drink).. Why do some women wait until its too late to report the abuse? Why is it that most abuse victims refuse to press charges?? or if they do, they have them dropped later on...