I had an affair after being married for nearly 28 years.I KNOW it was due to impulsivity as well as a desire to be seen as a smart, sexy woman (something my husband had long forgotten.) My ADD soared as my hormones dropped at age 55.
Failure to appreciate the impact is also part of the ADD legacy in my case; my relationship has been destroyed with 27 and 29-year old children.
Your spouse needs therapy with a doctor who understands ADD. Good luck!