Is my husband's texting with old girlfriend a symptom of ADHD??

So yesterday I came home from a work trip, having been gone a week, only to discover that my husband had been texting with an old girlfriend.  These texts were what he calls "harmless flirtations" - but I call establishing a social media relationship with an old flame.  The texts went well beyond minor flirting and into a level of intimacy and of a sexual nature that are totally inappropriate.  He tells me he is sorry and is struggling with this because he is an "affirmation junky" and was really just reaching out to get this positive feedback (we have ben having ups and downs in our relationship over the years, but thought we were on an upward swing having recently begun to learn more about ADHD and how this has been impacting our relationship).  I don't knwo what to do - I feel like one of those women on the made for TV movies who are totally unaware of the level of deception in their relationship...

We've had issues with trust in our relationship - and in fact I had discovered he was texting with this women a while back (these texts were relatively minor) and had a big blow out about how much this hurt me (this woman threatened to show up at our wedding 15 years ago and object) and asked him to stop all contact with her.  He said he would - but because we have trust issues, I didn't believe that he actually would, so I would look at his text messages.  This is how I discovered his latest email trail with her - apparently he forgot to delete it before I got home from my travels.  He says he is sorry but there is nothing for me to worry about (she lives on the other side of the country)...

I'm so sad and confused...what do I do??