IMHO, any A is the fault of the perpetrator. No matter what the marital situation, an A is a choice between two people, one of which is OBVIOUSLY not the spouse.
Regardless, though, I have come to discover that no one is perfect, and there is always room to improve. I also believe that if you even have a friend of the same sex, who is not a romantic interest that comes before your spouse, that potentially could be the equivalant of an EA.
When it comes right down to it, somewhere along the way one spouse forgot to put the other first, forsaking all others.
Im still standin better than I ever did looking like a true survivor feeling like a little kid Im still standin after all this time and Im picking up the pieces of my life without you on my mind..