I don't have HIV or AIDs. I am in a magnanimous relationship with my boyfriend. We both get tested every other month. Not just for aids, but full STD panels. Why can't I give blood? A good answer...
HIV is a retro-virus. Retro-viruses are harmless, everyone is full of them.
HIV will eventually turn into AIDS which will kill you (it actually makes it easier for sickness to kill you, but the point is still there). If you have HIV it
will eventually turn into AIDS.
This isn't strictly true - but is in practicality.