also, Finchelet, I am curious about "the mirror being the universe". It may be that this is a safe place for a dissociative part to be out? I get that the cutting is a way to "cut off the emotionally repressed part of you". It's a symbolic act though. It's a shame part of you cutting of the part that was hurt, or "stabbing the part that is loathed. Does your therapist understand that you dissociate? Another interesting thing that you talked about, "making the comic books". In a way this is an interesting containment of the dissociation. Look for the movie, "Crumb" goole it, and see if you can find it on YouTube or netflix or pay per view? Anyway was a psychedelic artist from the 60's movement; and if he didn't draw, he would get very depressed; almost like his Id part of his personality was coming out in the art? His father was physically and emotionally abusive.
Again, if you started cutting earlier than the group assault, obviously the later trauma only increased the triggering of the earlier maybe. It's that part of you that might be cutting now? It is treatable. Do you understand "mindfulness"?