Is Billy really to blame?

In the beginning of the book, Billy is consumed by his guilt for killing an innocent woman. He thinks about the accident constantly and it soon takes over his every thought. As the book progresses, Billy seems to feel less guilt about the incident and starts to think that his wife is responsible. He tells Hopley, "It was my wife's fault; because of what she was doing to me" (Chapter 12). Billy hit and killed the old gypsy woman with his car while his wife was giving him a hand job. He also goes on to blame the old gypsy woman claiming that "She came out from between two parked cars, didn't look either way. They teach you better in third grade" (Chapter 12). I find it confusing that Billy can go from being consumed by his guilt to blaming everyone else involved besides himself. I was reading this article about psychology and how people tend to deal with guilt and it reminded me of Billy. According to Mother Me, (excuse the weird name, it's actually a pretty interesting article) the first stage of guilt is feeling apologetic. Billy was definitely apologetic in the beginning of the book. He was not only haunted by the memory of the gypsy woman, but he felt guilty for putting his family in a bad position. He had given his family a bad reputation and Linda was ostracized at school. He tells Linda, "I heard you've been getting some pretty rough handling from the other kids. I'm sorry about that" (Chapter 1). Billy was enduring the first stage of guilt with his apologetic mindset toward everyone. But by chapter 12 he has transitioned to a combination of stage 2 and 3: defensiveness and the tendency to make excuses. He blames the gypsy and his wife and refuses to believe that he is responsible. The next step is absentmindedness, which I can envision Billy doing. He will probably try to suppress his memories of the incident by binge eating. Do you think Billy should be blamed for the accident? Or is his redirecting of the blame toward others justified?