If it’s HHV reactivation, then ME/CFS isn’t contagious.
For one HHV-6B is listed on some official list of empirically validated ME/CFS triggers. I don't remember where I saw it. But I will let you know if I see it again.
I base the idea that ME can be infectious on my own experience and the observation that there are many families and couples where several who are all ill.
Viruses and bacteria have very different capacities at being contagious and also different pathways of infection. For herpes it is mainly saliva but there is also sexual transmission (especially HSV-2).
Under normal circumstances the immune system can control HHV-6B. But the immunocompromised often can't.
If you have a situation of ongoing distress, an illness or an infection as far as I understand it your HHV-6B will always go up a little bit because your immune system is a little bit compromised at controlling reactivation. See here where it is suggested that HHV-6B loads in saliva can be used as a predicter for athletic fitness to be used in training plans for sports medicine.
Salivary human herpesvirus 6 and/or 7 (HHV-6/7) have recently attracted attention as microbiological markers of physiological fatigue in laborers and athletes. However, the accuracy and efficiency of the HHV-6/7 assays can be improved for practical application. We conducted three experiments to...
pubmed.ncbi.nlm.nih.gov
If in such a situation you manage to get high loads of HHV-6B DNA additionally from outside in the form of a reinfection by the means of a kiss with an acute ME-patient (with PEM) your immune system might be overwhelmed and reach the criticial ME-threshold and you end up having your first ME-flare.
I think that that's what happened to me.
I know I can't prove it, of course. But it doesn't contradict any logic.
I am open to auto-immunity theories. However, I find them much complicated than the simple idea of HHV-6B reactivation causing ME. However, for me personally auto-immunity theories fail to explain why I can bring my ME flares (yes, I fulfilled CCC and I have PEM), fully under control with the antiviral acyclovir. And HHV-6B theory can. Acyclovir has not excellent but good activity against HHV-6B.