The sexual activity is very possibly unconnected, no one knows too much about XMRV transmission but with HIV for example the risk of female-to-male transmission is only around 0.04% per act. http://www.ncbi.nlm.nih.gov/pubmed/19179227
Before i came to this forum i was in thebody.com and at poz.com because mi first concern was HIV and many many people that went to these sites when they got sick after having unpotected sex kept testing negative for HIV for months even years and guess what? the vast majority of them are now testing + for XMRV many people kept thinking they had some sort of undetected HIV strain because a lot of them have had many OIs and other symptoms like candida, swollen tongue, brain problems including lesions, skin rashes, IBS, neurological problems, dry skin, and the list goes on and on..im telling you all retroviruses have the same modes of transmission that would explain why there's CFS "outbreaks", the good thing about this virus is that it doesn't seem to affect the number of lymphocytes that's why many people with CFS went on struggling for years getting all types of responses from Doctors including the most typical ones " it's all in your head, u need a vacation , you are stressed out" because the lymphocyte counts is the very first thing Drs look at when they do a CBC if they look normal they assume right aways you have no infection of any type.