The mother was responsible for Bob's destructive behavior.

it's like what came first, the chicken or the egg? did his destructive lifestyle come because his mom didn't love him, or did his mom not love him because of his destructive lifestyle?

considering the boys were half brothers, i'm guessing bob's issues stemmed from genetics on his father's side and were unavoidable.

I would definitely not go as far as saying that the mother was responsible for Bob's behavior. Of course, who are we to know? But from what I could tell, Bob had a very impulsive and addictive personality, and if you've ever been around someone like that, you know how difficult it is to have a happy and healthy relationship with that person. From what I saw in the movie, she did try to be a loving mother to Bob, but he made it as difficult as possible for her. And did she try hard enough? Maybe, maybe not. Also, at this point he was 21--an adult. So there's 21 years of a back story that we know nothing about. And I agree with the other comment, which came first... the chicken or the egg. I'm sure only the Valenzuela family knows the answer to that. So let's not throw out accusations.