Abuse is bad enough the shock of someone you have trusted and thought well of or even have loved suddenly turning against you and on you for no reason at all is shocking enough. But it doesn't stop there. In order to minimize or trivialize there abuse abusers do like to bring in other people to share in the abuse.
Co-abusers fall into three categories. The first, is out and out support for the abuser, these people gain almost as much pleasure from the abuse as the abuser themselves. It's abuse without comebacks or responsibility - they argue the case for the abuser because they want to hear more about the abuse - and then they take that information back to the abuser who offers them a little bit more - and so it goes on. In the process they hope to show the abuser what a good friend they are to them - and hope for some kind of reward. It usually stops when the victim or survivor of the abuse realizes what they are doing.
These kind of people are potential abusers. They are learning the black art of abuse. Building up their confidence and seeking out there victim. If they don't find a vulnerable person to abuse - they might give up - they will forever be co-abusers - but the real lesson they have learned from the abuser is where to look for victims. And survivors of therapy-abuse are perfect - how can you damage 'A badly damaged person' a bit more damage is not going to make no difference.
The second category of Co-Abusers - is those who have learned about the abuse but who have been told by the abuser or more likely the co-abuser to keep quiet. "You can't change anything." "What is done is done." "It's all for the best.". It makes them feel uncomfortable - but no more than that. When the abuse finally happens they feel a degree of sympathy for the victim - but because they do not want to get involved - and distance themselves from the victim. In time they hope that the victim will understand - but the shame of knowing and not speaking out keeps them away from the victim.
The third category of Co-Abusers are those who are on the side of the victim - or so it seems. More often than not they dislike the abuser - but have only limited sympathy for victim. The sort of things they would like to say are. "What do you expect." "It's your own fault." "There must be something wrong with you."
What all three types of co-abusers should remember is that by supporting the abuser or keeping secrets, or trivializing or minimizing the abuse - they are not only adding to the abuse - of the victim. Who for whatever reason is not good enough to gain there support - they are encouraging the abuser to repeat the abuse.
What will they say to the next victim of that person abuse. "We didn't know." You did know! Survivors go to great lengths to get people to listen often to the detriment of there own well being. Perhaps they would like to blame the last victim for the abuse. "It wasn't explained well." Here's a simple test for this one. Tell someone you don't know that well about what happened. They will react with disgust - guaranteed. Then ask them again 6 months later - and the same thing will happen again. Abuse is very easy to understand - but you need someone who wants to listen.
Finally - here is a test for co-abusers - the person you are defending, protecting, shielding, making excuses and denying for - would you be happy for this person to give therapy or provide support to another friend. A vulerenable person in need of help?