1. I don't think that's true -- unless some ridiculous percentage of the population of Southern Africa is bisexual.
2. Even if it were true, so what? Do women control who their husbands cheat on them with? Regardless of whether their husbands get HIV from prostitutes, from local floozies or from other men, they still get the disease. In the long run -- at least from the woman's perspective -- it really doesn't matter.
I’m just guessing here, but I’d be willing to bet you don’t know the transmission rate of HIV from female to male, vs male to female or male to male.
In fact, I doubt you have a clue. For someone who doesn’t know the amount of money spent on HIV research vs the other MAJOR killers, doesn’t know why universal precautions are mandatory now when they weren’t 30 years ago, and who doesn’t know HIV transmission rates in varying demographics, you have a remarkably one-sided viewpoint.