I could have written this post, I understand exactly where you are coming from.
In my own journey I have learned that this is only about ME, not my friends or family etc... I have to decide that I want to have a better life and stick to it, with firm resolve, no matter what other people say or do. Part of that involves not putting myself in situations where I feel tempted to drink/do drugs or frustrated that everyone else is and I "can't." I am trying to build a new life for myself, full of positive friends that lift me up rather than drag me down, and full of new interests and pursuits that don't revolve around alcohol/partying.
If I were you I would just tell your friends "I need some me-time and a break from drinking and partying. I will not be attending any events or get-togethers that focus on alcohol or drugs. If you would like to get together for coffee, to go to the spa, to go to movie, etc. [fill in the blank with some things you like to do or would like to do that don't involve drinking], I would be happy to do that. Otherwise I will not be able to make it." (You could even tell them not to invite you, so you won't have that temptation).
I know it is hard to feel "left out" but you have to do what you have to do to move forward with the life you want. Best wishes with your goals.