Seek, don't beat yourself up over the should haves, because honestly, no matter what you did differently, it wouldn't have made a difference. He isn't an alcoholic because of anything you did or didn't do, he is an alcoholic because he has made certain choices and has not decided to actively seek recovery. Even if you could go back in time knowing that he would turn into an alcoholic, you still couldn't prevent it from happening because you just aren't that powerful. None of us are.
Have you thought about going to counseling to talk about these feelings with a professional? I understand the anger and pain, but it isn't healthy to let the anger take over. Although your grandson has chosen to not seek recovery, that doesn't mean that you should allow his choice to effect you so negatively.
The last thing I would like to say is that even though you disagree with how he is living his life, it is his life to life. Everyone should be given the dignity to live their lives the way they choose, and although we hope that our loved ones will find recovery, that is up to them.