An enabler is a person who tries at all costs to soften someone else's blows and takes on the responsibility for someone else's actions and attempts to minimize the problems of another, usually a loved one. This is quite frequent when addiction of any type is involved. If you are the nurturing type, than you are far more likely to get caught in a cycle on enabling. Just remember that you are doing more harm than good with all your help.
Stop doing anything that allows this person to continue on with his current lifestyle. This includes lying or covering up for him in any way.
Stop taking on this person's responsibilities and claiming part in her actions. She needs to learn to be responsible for her own actions.
Tell this person you are finished enabling him and that you have set clearly defined boundaries that you are not willing to cross.
Do not react to anything that this person has to say regarding her problem. From such a subjective point of view, she won't understand that a problem exists.
Stop giving this person money, loaning him money, lying for him or calling into his job for him. At some point, there will be a reckoning for his lack of accountability, and by aiding in his bad habits now, you are hurting him in the future.