With a good and adequate nutrition and some activity like doing some sport your body creates more cells and T-Helper cells to delay the infection of aids.
Yeah but that delay isn't nearly enough to stop it. Maybe extend your life by 5 years but once HIV mutates and leads to AIDS you're forgeted. Currently all you can do is delay it.
The problem with HIV is that it mutates and you can never really get rid of it. It sneaks around your body's defenses through a long chain of mutations and eventually reaches the white blood T cells, which it then infects.
Once this occurs, it's irreversible. HIV eventually mutates again leading to a hyper-efficient infection of the T-cells which your body can no longer recover from, you lose immunity defenses and you die. You cannot wake up one day and say "Hooray I'm cured and don't have HIV anymore!" you still have it. Your body can't kill it off and there is no known vaccine or cure against it. You CAN delay it though, but you're still always infected (see HAART).