to try and give a useful answer this time:
the reality is that if you, a (relative) outsider, try and come between a group of people and the abuser they consider a good friend, you are very likely going to lose. you can try to force the issue but ime you are going to see them close ranks and possibly freeze you out entirely, depending on the level of control their group has over the scene. none of this is to say "don't try," just that you should prepare for things going poorly.
an anecdote: when i was a kid my friend group was the heart of the party scene in our town. two of them ended up being pedos. no social consequences.
i think it's good of you to try, mind.