I think this is more of an individual question that you have to ask yourself but, something that I can help you with is how to support them. If you have a friend that has hiv then you should support them by getting them the correct help. you should be there to support them in any way they need, but at the same time you need to make sure that they are getting the right information and resources that they can. As for how you should react, everybody is different with how they deal with hard subjects so it really depends on you and your personality same with how you would feel.