You ask deep questions that only the two of you can answer - although the help of a good couples therapist could also be very helpful. It's a beautiful article, only thing I'd change is I wouldn't compare it to an affair. Affairs are about intentional deceit. Very, very different.
When we get married we take vows for life. This is a questionable practice and a bit of a set up as it is, but in your case you actually acknowledged, from the beginning, that people change and you knew you might. There was no deceit here. Just life. Sometimes life has pain and challenges in it