Jakers,
You can't MAKE him do anything. All you can change is yourself.
You'd be surprised how strong you can get. You've been pretty strong, anyway, living with this mess for so long.
Don't worry about leaving or not leaving right now. Don't worry about what to do to get him sober--there isn't much you can personally do. Contrary to what you told him, you are NOT the best support he has--other alcoholics are. As much as we would like to help, it's difficult to realize it but there is very little we can do to get someone else sober.
What you need to do is to take care of yourself, and you WILL get stronger. You don't have to leave him unless you decide that is what you want for yourself. Nobody will tell you what you have to do.
Please try some meetings for yourself. Really. They can help.