(All names have been changed)
When I started college almost 3 years ago, I met my then-roommate Grace. She and I became best friends very quickly and lived together freshman and sophomore year. During our freshman year, I was sexually assaulted by a mutual friend of ours. A couple months after the fact, when I was finally ready to start talking about it, I told Grace what had happened. She responded with a combination of shock and disbelief. She told me she was sorry, and that I could talk with her about it if I wanted to.
In the next couple months, and into the beginning of sophomore year, I noticed that Grace continued to hang out with my rapist, talked about him to me, etc. Considering what close friends we were, I felt very betrayed by this. I basically told her that I found it really shitty of her to continue amicable interactions with this guy after knowing what he did to me. We talked about it some more, and it turned out that she never really believed me when I told her what had happened. She spewed some victim-blaming shit about how it was "probably just a misunderstanding" and that she "can't really believe that he would do something like that." I was appalled and said the fact that she wouldn't take my word for this was abhorrent. I finally said that she was an adult and could choose to stay friends with a rapist if she wanted to, but that he was not allowed in our dorm, and that I did not want to ever hear his name from her again. She agreed to this. From what I could tell, she seemed to fall out of touch with him. Whether this was intentional or not, I don't know.
Later on in the semester, she had a pretty traumatic experience that she didn't label as sexual assault, but, to me, seemed nonconsensual. She had brought home a guy she had met at a club (I saw him in the lobby of our building and didn't like the look of him at all). When I saw them together she was rather drunk but was talking clearly and standing up straight. I took her aside for a moment and asked if she felt she was in the right state to hook up with him. She said yes, so I felt like I had done my job as a friend looking out for her safety.
She brought him home, they ended up having sex in the other room, and from whatever I heard through the walls it seemed fine. The next morning, I saw her in the living room crying. I asked her what had happened and she told me that she never wanted to have sex with him, but that he kept asking repeatedly and pressuring her until she gave in. I was very supportive to her (let her talk, let her cry, assured her that she was not to blame, etc.). Later that evening she thanked me for being so supportive, and apologized for not doing the same for me when I was sexually assaulted. She told me she was sorry for not taking it seriously before, but that she now understood and believed me.
A few months later, I decided to report my assault and pursue a Title IX investigation (look it up if you're not familiar with it). Given what she said to me most recently, I thought I could rely on her to back me up and testify in my favor, corroborating that I did, in fact, tell her that I was sexually assaulted by this person, and that she believed it to be true. Weeks went by and I got a nice email from the University saying that he was found not guilty, along with a report containing all evidence and testimonies. In it, I saw a summary of her exchange with the investigators. To my shock and disgust, she told them that she didn't believe me and essentially testified in favor of the rapist.
It goes without saying that I no longer considered her a friend after this point. I spoke with her about it shortly thereafter. She honestly seemed oblivious to how bad she made me look in her testimony. I asked her why she told the investigators what she did, and as we talked more about it, the same old victim-blaming shit came back up. She said she "disagreed with labeling the experience as sexual assault" even though I had clearly told her exactly what happened (things were happening, I asked him to please stop, he kept going). For whatever reason, my so-called friend was unable to take my word for my experience seriously. After that, I continued to run into her in the building or on campus. She'd smile and say hello, but was the last real conversation I had with her.
She happens to be the girlfriend of my very good friend, Brian. I introduced them when Brian was looking for a drummer for his band (Grace plays drums). Up until now, I didn't tell Brian anything about what Grace had done, because I figured it was strictly between me and her and not his business. I found myself wanting to open up to him about it, because I want to be honest with him about important things. Also, because this is his girlfriend we're talking about, and what she did, IMO, speaks volumes about her character. Still, I said nothing.
Tonight Brian and I were talking, and he said, "By the way, Grace told me she's worried that you're upset with her." I didn't want to be like "Yep!!! She's a rape apologist!!!" so I just said, "She can approach me personally to talk about it if she wants to." and he said fair enough.
I don't know if she will reach out to me, but the ball is currently in her court. My question to you is:
Since Brian brought this up, can / should I tell him exactly what happened?
A part of me really wants to, for reasons stated above, but I also don't want to be accused of trying to "start shit" or deliberately damage a relationship. They've been together for over a year now, and seem pretty serious. I feel like this is important information for him to know about what kind of person she is. I know Brian as a person, and he values knowing the truth above all else, but I'm still torn. Help?
tl;dr: Ex-roommate testified against me in a sexual assault case, her boyfriend (my close friend) mentioned to me that she thinks I'm mad at her, I'm not sure what, if anything, I should tell him about this.