What I am saying is not about people who catch diseases, etc.- HIV/AIDS will kill somebody, there is no doubt that can cause PTSD. I am only talking about someone cheating. No diseases, no abuse, no forced sexual encounters, just finding out your partners has been cheating and being hurt by that. When there was more to it than the cheating- catching a disease, being pushed into sex, or being abused- the yeah. Finding out they've been cheating and then breaking up because they betrayed you- I don't think so, because the definition of PTSD doesn't class that as something so extensively traumatic as something that has threatened your life.
I'm not very good at explaining things sometimes so I hope that makes sense.