No, I don't.

I mean, I someone I know could have HIV without me knowing it.

No, there is no reason to avoid that person. HIV isn't contagious except through unprotected sex, from mother to fetus, or blood transfusions.

About three weeks or so after transmission, many but not all get initial symptoms caused by their immune systems fighting off the virus. The immune system is normally capable of suppressing the virus very well in the initial stages of the infection, which is why the viral load that spikes in the beginning normally remains low after the initial stage. In the beginning when the viral load has built up to a high level, the disease is relatively contagious (not in normal everyday situations except for unprotected sex). That is probably a major reason why such a large proportion the populations in Southern and Eastern Africa have HIV. It is fairly common for people in urban areas in Southern and Eastern African countries to have concurrent multiple sex partners. A person who gets HIV is unlikely to know it until the onset of the initial symptoms if they even occur. During the initial period of high viral load they may infect sex partners other than the partner who infected them. There prevalence of HIV is very high in that part of the world. In most parts of the world, HIV never became an epidemic outside of intravenous drug users and male homosexuals.

More information:

https://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2804%2916606-3/fulltext

https://www.avert.org/professionals/hiv-around-world/sub-saharan-africa