This sounds more like you are trying to control your friend than setting boundaries for yourself.
You have no control over him. He is free to go under the influence, hang out with anyone he chooses and talk about his friends. This includes showing up at a concert with his friends, assuming the host does not mind or it's a public venue.
If you don't want this to be a part of this, take responsibility for yourself and remove yourself from the situation.
We all have the potential of going under the influence of something. Short of living in a cave, not sure how one isolates from other people's potential behaviors.