I've messed up. What do I do?

Honestly my TWIN sister always tries to get me to smoke pot and i have never tried it even once. You aren't responsible for the decisions your sibling makes. Even if you did somehow force him the first time, he is completely responsible for what he chose to do once it was over. My sister's personality is completely different now and yes it is becuz of the pot. some ppl can handle it and somewhat maintain their life while others cant. I personally think you should talk to him or talk to an adult becuz trust me from my own experience, it is a really hard thing to live with and even doing the hard things like detox may just be the best thing in the long run. I hope you have some luck.