You quoted up pretty much what you should do: talk to him about it and say why you are feeling hurt. Make sure he understands that you aren’t hurt by the diagnosis but more so by the secrecy around it.

And from now on, if you choose to stay with him (and while this is a great ordeal, in due time you could forgive him if you don’t test positive, from what I read in between the lines), I believe that you could be there for him, and your relationship could grow. I honestly think he was too scared to tell you, that you might runaway from him.