I have been here for donkey's years but given the nature of this post, felt it best to change usernames.
Long story short, my daughter (early 20s but slightly vulnerable) is currently visiting her boyfriend abroad. They have been in a long- distance relationship for several years now. I have my concerns about the relationship - some red flags which I have discussed calmly and openly with my daughter - but they're in love, and for the most part anyway, it's going ok. They have a very intense relationship.
Anyway, the other day I received a fairly strange message from him (I am fluent in his language), saying that my daughter was hiding the truth about something, that she had been raped when she was 17. Obviously I phoned her straightaway to gently try and get to the bottom of this. In the background, I could hear him say to her 'tell her the truth' in his language. I honestly think he considered himself some sort of saviour for breaking the silence 
My daughter admitted to me that it had happened, but didn't want to go into details on the phone. She said that she had made her own peace with it, and had resolved it in her own head. I didn't know if opening an old wound was going to make things worse for her, and because I wasn't there to hug her, I agreed to let it drop and talk about it when she gets home.
Her boyfriend was in shock but apparently said some arsehole things to her (he sometimes drinks too much, which doesn't help) such as he thought he was the one who took her virginity, and did it really actually happen, or was she just saying it for attention. So she had this to deal with, as well as the fact that he'd told her secret to me.
I messaged him and told him that it was not his place to tell me, that I was incredibly upset but could do nothing to help her from here, that telling me was a breach of her trust and privacy (as she must have had her reasons, I guess). And finally that if he was going to keep drinking and not support her in the face of this revelation, that it would be best if she came home.
So there is a lot to this mess, but my main question is, how do I best support her when she gets back home? I just KNOW that she is going to downplay what happened when she was 17, and won't want to talk about it. I told her that she might think she has processed it, but has only suppressed it, and it's best to deal with it in case it bites her on the bum one day. I know that she will refuse to go to the police, and that is absolutely her choice. I will respect her decision and support her no matter what.
But how far do I mention the rape? Do I delve? Do I leave it? Is it enough to say that I am here for her always, to support quietly or talk about it? Or is that too hands-off?
I am a single parent and I know with absolute certainty that she won't want to tell her father. Or probably anyone else. But that means that I need help from you wonderful lot 
This is a first from me. I don't know how best to handle it. I am devastated that this should happen to my amazing girl. I am so disappointed in her boyfriend's reaction, but I hope that what was initially misplaced anger, has now settled into something more nurturing. I think this will be the case.
She and I are so close. We have a wonderful relationship. And although this isn't about me, I'm now doubting myself and thinking that I must be a shit mum as she never told me. I keep thinking back, but don't remember any major changes in her behaviour at that time.
Please help.