Ummm,
A) If you have unprotected sex at any point in your entire life, no matter how much you think you trust and love a person, you are at risk for AIDS. This includes if you are married.
B) AIDS is not preventable if you do not know how to prevent in, which in many places in the world the governments and/or religions do not allow for correct treatments. For exmaple, in some parts of Africa, people think AIDs can be cured by having sex with virgins. This isn't becuase they're stupid, but it's because it's what you've been told is true.

AIDS is bad. Cancer is bad. Let's fight them BOTH.