But what makes hiv able to avoid the immune system?

Hiding inside cells: The HIV is able to avoid the immune system because of its ability to hide inside the cells. The antibodies your body makes to prevent future infections cannot enter the cells, thus they are useless once the HIV is already inside. While inside, they can multiply and thus continue to cause disease for years. So, the best treatment we have =prevention. Live well, evangelineli1. Good luck.