People who think they can change someone else, whether they be the MJ-intolerant GF/BF or the MJ-loving GF/BF, are doomed to lead pretty unhappy and unfulfilled lives. People do change of their own accord, over time, but they almost never do so because of feeling forced into it by another. If you've had multiple discussions with them about something...anything, especially drug use, and they're position is not showing any signs of changing, then it's a pretty safe bet that it will never change because of anything you say. At some point, you just have to admit to yourself that the way they feel is the way they feel, and act accordingly. For me, this would mean breaking off the relationship. For others, it might mean changing their lifestyle to no longer include MJ. The only thing that people truly have any control over in this life is themselves. Stop trying to change others and focus on yourself and what you want out of life. If your life isn't complete without MJ in it, then you are doing yourself a disservice staying with someone who hates it.