What if I'm thinking of not telling the girl I have HIV before sleeping together?
Why would you do that? You would risk giving her a disease?
I don't want her to leave me because of that.
Not telling your partner that you have an STD is such a terrible thing to do. If you end up passing it onto them, they'll be devastated and they should know the risks of sleeping with you so they can make the choice themselves.
You should just mind your own business when I'm thinking of sleeping around.
It's your responsibility to inform your partners about you having HIV. You need to stop sleeping with people until you find the courage to do so. Intentionally keeping this information from others is illegal and you can be sued because of it.