Welcome to SR--I think you'll find a lot of help here. Everybody here "gets it" and is glad to share their experience, strength and hope. One of the first things I'd suggest for you is to read as much as you can here, being sure not to miss the stickied threads at the top of the page. Educating yourself about alcoholism will go a long way in helping you understand what's going on and what you can and can't do about it.
Here's a link to a thread from the stickie section to give you an idea of what kind of information you'll find there:
http://www.soberrecovery.com/forums/...l-problem.html
I'd also suggest you look into Alanon. SR is a wonderful, supportive community, but it's not a bad idea to have some real-world help too. Here's a link to help you find a meeting:
http://www.al-anon.alateen.org/ Many here have found Alanon to be a great source of education and support; you may find the same.
You say you're afraid of the addiction and where it will go. Well, alcoholism is a progressive disease, and he will indeed continue a downward trend, just as you fear. As you say, you can't make him get sober, either. What you
can do is educate yourself and find support here and at Alanon. As time passes, you'll start to see more clearly and you'll begin to know what you want to do. Please don't feel you need to rush into any decisions or actions right now. Get your feet under you first.
Again, welcome to SR, and wishing you strength and clarity.