I personally think that no it can't, and almost every definition of PTSD I've seen has specifically said that although a break up can't be traumatic, it does not cause PTSD.
For someone to be diagnosed with PTSD they are meant to have experienced something that implied death or severe physical or emotional damage, i.e. a war, car accident, child abuse, rape, coming across someone who has been killed or committed suicide, etc. and have a certain amount of different symptoms (there are 2 or 3 groups of different symptoms and you need to have a few symptoms from each group, nightmares, hypervigilance, avoidance, flashbacks, etc.).
If the infidelity was part of something bigger, e.g. abuse, then it can add an aspect to the PTSD. But infidelity alone doesn't really threaten your life like a war or abuse does.

Having said all of that, the trauma of infidelity shouldn't be downplayed as you've been hurt, humiliated and betrayed.