What ive learned is the more you pressure people on it or keep screaming at them. They will just use it as an excuse to get coke. But its up to you how you address the situation. I was like that when i was 16 on cannabis. Idont touch it now. But i was a nightmare for my mum and dad. Which i regret. But i grew out of it and quit hanging around with using mates.
Have you asked him does he want to quit? You obviously cant make him to. You will get nowere. He will soon realise like i did. But id set a few ground rules for now. Like u dont want it in the house.
Least running will help you as well to clear your mind of things. Dont give up on that lol