Ok breathe.......
I do understand how disturbing it is when the minor living your home smokes pot. That is where my son started but he was a lot sneakier about it. I do understand the confusion you are feeling since everyone around us smokes pot. I live in a State that just "legalized" it (ha......how can a State legalize something that is against Federal Law--the can of worms that has been opened is ridiculous). It's hard to say something is "wrong" when a majority of voters disagrees. It's easy to begin to doubt ourselves when we're in the minority (or so it seems).
So....what to do.....I don't have answers for you. He may grow out of it. He may not. I think the most important thing I could have done early on with my son is to not enable him (which I did...unfortuantely). I wish I had allowed him to deal with the consequences of his decisions early on. But I was always there sweeping up the messes he made for himself.
I think the thing I would stress to you more than anything from your post is you are NOT a bad mother. You're a mother who wants the best for her son. But unfortunately we can't control another human being. Please......do the best that you can......and don't beat yourself up. That doesn't do anyone any good.......particularly not you.
Keep going to your meetings. Keep taking care of you. He will either "get it" or he won't. Stay calm because getting all worked up does nothing but fuel the fire. I have found the calmer I stay, the more impact my words and actions have........anger is an illusion of control.
I remember how difficult it was when I first found my son was smoking pot and drinking. It was exacerbated because while my husband and I were spouting "say no to drugs" jargon, my AXH was passing him a joint.
Take care of you.
gentle hugs
ke