This is the first time I've come across someone dear to me having a drinking problem. Honestly, I feel a little guilty for not seeing the problem in his condition earlier and supporting him before he got to the point of alcohol addiction. I hope it's not too late to make things right.
I don't think you shouldn't blame yourself for anything. No matter how close you are, you each have your own lives and it's not always possible to track down problems of this nature in time. You can support him now, though.
I'm sure that if your mate has the will to deal with the problems, there's a very good chance things will get better. First of all, find a reliable rehab centre that provides comprehensive addiction treatment as well as various programmes aimed at addiction treatment. There's a lot to choose from now, so I think you'll find the best solution.