That's a tough situation to be in. But you are absolutely not responsible for his decisions and I guarantee you that you cannot force him to make a decision. He has to make the decision to stop on his own or it won't stick. And please don't feel bad if he doesn't do it "for you". The addiction is stronger than a lot of things - I lost two relationships because they gave me drinking ultimatums and I walked away because I didn't think I had a problem. The most important thing is to protect yourself. Going to Al-Anon is a good step.
Mail him his key. Do whatever you need to do to make yourself healthy and to stop feeling responsible for his choices. Counseling for co-dependency is a great step also - it helped me immensely, and I hope it helps you also. Stay strong!!