Don't be scared.
We have a very cool page that tells people what to expect at their first AA meeting, and I found one that does the same for Al-Anon:
What to expect at your first Al-Anon meeting. You don't have to say anything if you don't want to, but it's good to at least give your name (first name) and to let people know it's your first meeting. It's even OK to say that you are nervous and would rather just listen at this meeting.
You will meet a lot of people who understand EXACTLY how you are feeling. For that alone, it's a great relief. You will start to feel less alone, and to see how others cope with some of the craziness that goes along with living with an alcoholic. You will start to lose those feelings of shame as you learn you didn't CAUSE the alcoholism, that you can't CONTROL it, and that you can't CURE it. You can, however, make your own life much better.
I've been in Al-Anon during two periods of my life when I was living with alcoholics, and it was a real lifesaver. I'm in AA now for my own drinking (which ramped up once I was no longer dealing with other people's issues), but I still use the lessons I learned in Al-Anon to detach from the unhealthy behaviors of other people.