When an addicted loved one is exhibiting increasingly alarming behavior, first of all, don't take it personally. Remember, it is not directed at you. This, unfortunately, the face of addiction.
If I had to characterize pot users in one sentence I would describe them as observers of their own life. This passivity cripples ambition and motivation. However, a strong relationship keeps the bridge open between you and your loved one, and this will be vital when they signal a desire to change.