Aquarius, I have found for my life -- honesty is the BEST policy. I don't know if your friend is already aware of your problem with cocaine, and if they are it might make this process a bit easier, but if they are a good friend perhaps an explanation, and an apology for their discomfort may be in order. I don't know how comfortable you are about addressing the elephant in the room but I know in my life -- just fessing up to everything and apologising for my actions is probably WHY I still have the people I do in my life. People can be pretty forgiving if you're honest, you don't make excuses, and they actively seeing you try to make a change.