i totally disagree with the above poster.
there is absolutely no reason that you should have to limit the amount of time your brother is left alone with your son when it is obvious by your post that he loves spending time with him.
your brother's sexual habits have no bearing on what kind of uncle he is to your child. hiv is NOT transmitted through kissing...even with chapped lips.
First of all, if your brother suspects that he may have been exposed to HIV he should test three months after his last possible exposure.
Secondly, there is no risk to your son from what you have described. HIV is transmitted by unprotected vaginal and anal sex, or by shared needles and from mother to child.
However, I think you are being hard on your brother. He may be very scared about his status. Calling him "disgusting" is unfair and not very helpful. If you have further concerns about the beahviour of your brother towardss your son, that is a matter that can't be dealt with on this forum. And I would suggest speaking to social services, or reduce the amount of time your brother is laft alone with your son.
As for HIV risk in this situation; none at all.
HIV is transmitted by unprotected sexual intercourse, so even this guy is infected there is no risk for your child! None!
I recommend you not to worry about your brother being infected with HIV, they can't transmit it to you unless you have a sex with them. As long as he is having protected sex, he can sleep with many women & men and still won't have HIV.