I want to start out by saying that I’m very sorry that this has happened to you. I’ve been through similar circumstances — my ex-husband, whom we discovered has ADHD after the divorce, cheated on me after we’d been together for five years. My marriage didn’t last as long as yours, so I can’t imagine how much more painful it must be for you because the experience was excruciating for me. To sum up, I sympathize.
I don’t think you’re completely wrong in your assessment. While ADHD and lack of impulse control could have greatly contributed to his poor choices, I don’t think it would have everything to do with it. Is he willing to go to marriage counseling? Are you? I can remember how easy it was to get caught up in “the heat of the moment” during our fiery separation and to let my anger poison my heart, but I hope that there is enough willingness in both of you to attempt to work through this difficult time.