<human>: My brother is in a physically and emotionally abusive relationship with his college girlfriend of 2.5 years. She is abusing him. I won't go into details, but there is documented evidence and witnesses that prove it is very, very real. 

I have researched how to be there for someone in this situation and the main advice I've picked up is to help them feel confident and supported and to NOT pressure them to leave the relationship or give them any kind of ultimatum. Despite my strong urge to shake him and scream "leave that bitch!" I have managed to abide by this advice and gently let him know I am concerned for him. The family as a whole is taking this tact for now. FYI I do not live in the same city as him so our relationship is mostly over the phone.

However, I really need guidance on interacting with his girlfriend, as she is still present in my family's life and will be there when I am in town. We previously were friendly, but I have not seen her since learning of the abuse. I have a serious problem with anyone who is violent; I simply don't want that kind of person in my life. Additionally, I am afraid that if I play nice, I am explicitly "approving" of their relationship when I very much do not approve. She has carefully concocted a sickening public image of a happy perfect couple. I really don't want to contribute to that charade.

However, I'm afraid that being absent from all situations where she is present or showing up and having a negative attitude towards her will: 1. make me the bad guy instead of her and 2. reinforce any feeling that she is all he has. 

I can't stress enough how concerned for him I am. I can easily see this escalating and him ending up arrested for defending himself, or worse. 

Help!

Can you condense the text into three sentences or less?
<bot>: How do I interact with my brother's crazy abusive girlfriend in a way that doesn't play into their creepy charade of perfection or make me look like the asshole?