A question about Aids/HIV from male-to-male sexual relationships

[Jordan0517]

This has been on my mind for a while and I havent done any research on it but today, in my life fitness class, we had a guest speaker who came to talk to us about STD's. Of course she brought up AIDS and HIV and she showed us a chart about the percentages of sexual relationships that are at risk. If im not mistaken, 53 % are from male to male sex..31% is from hetrosexual, and I forget the rest. = also remember from I believe wikipedia reading the female-to-female sex is one of the ones less at risk. So my question is: why are male-to-male sexual relationship at risk the most and does it play a factor into haterosexual relationships if these guys are having sex with both men and women? (please forgive me if I come off as ignorant of this. I was just curious and wanted to know because the thought of Aids scares me)