Yes, that's the nature of addiction really. A powerful beast within the mind, and not easily vanquished either. BUT, if the person struggling with the addiction is encouraged to persevere - and he may fall over many times - if he is encouraged to persevere [or she] then that's really all you can do. The rest is up to the individual. I liken the addict [I had a long struggle with substance abuse] to a lost soul who is on a journey to find and make him/herself whole - or at least begin to fill in the missing pieces - yes, missing pieces of the self - because the addiction has been filling in that space.

Encouragement and love - the rest is up to the person. You're a good friend to him.