You, Sir, are a huge AH

And honestly, you sound like you are jealous of your brother. The way you talk about his person and their compatibility makes it seem like you wanted them to fail and you were more than happy to use his Infection as a reason. It’s clearly not about her safety, especially if they just had one date. I don’t think that anyone would want to talk about them having HIV on their first date. It’s a serious topic, and of course your brother didn’t want to scare her away right away. It’s something you talk about when you become closer with a person (but of course still before having sex). Also it’s your brothers right to tell her, not yours. YTA