can being cheated on result in PTSD - no.
can being bullied result in PTSD - i think yes it can - depending on the circumstances - if you feel terrified and feared your life - then yes. and even though to an outsider, what happened when you were bullied (i.e. maybe you were cornered and had your schoolbag tipped out - to a child, that could be very threatening. more so if you grew up with abuse, as it would trigger unconscious fears of the same thing.
you say your past abuse doesn't affect you now - i disagree vehemently - i think the VERY reason you are struggling so much with being cheated on, and having the symptoms you are, is because the betrayal of the cheating (in the present) will at some level, be triggering the past abuse.
if you 'have' PTSD or not, isn't that important -= what IS important is that you seek help and work through all the issues and feelings you are struggling with in the NOW. maybe over time, the past abuse will come up as being related and you do release you have significant problems as a result of the abuse. or maybe, you wont.
either way - a label (whether or not it is PTSD or something else) doesn't change the fact what yoga re gong through is awful, and you need more support and professional help.
leave the argument of 'it is / isn't PTSD' and focus on getting the help you need.
cos, the 'funny' thing is - you don't actually 'need' to have PTSD in order to get real help ;)