I don't think it was Bobby's fault (although, I absolutely agree with Groovy that he seems for all intents and purposes to be a total scumbag)...And I also don't think it's appropriate to demonize the woman herself for falling into a bad place.
It's a scientific fact that our brains have a built in mechanism that tells us "It won't happen to me." I see it all the time..."I can do a little bit of heroin, or cocaine just this one time. I can stop whenever I want. I'm just having fun, letting loose a bit, I won't get addicted. I'm stronger than that, I've got too much willpower." If you've never really seen someone go off the deep end, then it's easy to overlook the fact that willpower and strength don't even factor in when it comes to drug abuse (which isn't to say that it doesn't take strength and willpower to say "No" or get out of it, but rather that falling into the trap doesn't make anyone weak or lacking in will).
Anyways...I don't understand the blame game that goes on whenever someone dies. There is no "what if," "could have," would have," or "should have." There's only what happened. Life takes us all out eventually. Whitney touched a lot of people, and it's sad to see that her candle burnt out so soon.