My best friend could be HIV positive and I don't know how to be there for them.

So I got a message today from my best mate who is gay and he didn't know who else to turn to, at first I thought okay probably a guy problem someone he likes blah, blah,blah crush, blah, blah, blah. But it went the complete opposite way, let me explain to you what's happened.We'll call him say..... Riley. Riley recently moved to Melbourne from Brisbane and one of his housemates, we'll call him James, lived there with him, also gay, basically James had the hots for Riley one thing led to another they're getting made out a few times etc. Riley had a test done before he topped James everything was fine, James had done the test the same time so basically the results came back negative how ever James' results were supposedly lost or misplaced. So today James receives a call from his doctor telling him to come in regarding his results, Riley found this out and started to worry because, Riley is allergic to Latex he didn't wear protection. Well James told Riley he's positive and basically they've had unprotected sex made out etc. My mind there is no way he can come out of this unscathed, it will be a complete miracle if he hasn't contracted it.My problem? I have absolutely no idea what to say I have no emotion, I'm shocked I'm not angry or sad I'm shocked the worse part is that before they had sex Riley was talking to me about how he liked him and they were sleeping in the same bed etc. so me being me said "Just fuck him may as well go all the way, he's already in your bed what more of a signal is that?"........................ Let that sink in for a moment. You can imagine how I feel, at the same time I can't imagine what in the hell he is going through, I have no idea what I'm supposed to do, how we are is we joke about things that have happened to us to make each other feel better, but there is no joking with this, he could be HIV positive and I have no words, there is nothing I can say that could make this thing better. So what am I supposed to do it isn't something like "Its okay it will get better" you can't say that it isn't going to be better if you have HIV you have almost no chance of having a normal life, I can't imagine what that would be like for anyone who is HIV positive.I told him I would get back to him in an hour after talking on the phone to him and I said to him I wouldn't treat or think differently of him no matter the outcome but what else is there to say, I can't even think of anything now and he told me hours ago. What do I do? What do I say?