Husband diagnosed with ADHD after having an affair - help

I'm brand new to this forum, and to ADHD. My husband of 20 years had an affair with a friend - someone I helped transition into the community when her family moved here and who was the mother of the child who became my son's best friend. We spent at least 3 days a week together via our children and friendship. I discovered 7 months ago that she and my husband had been having an "emotional affair" and sexting for the previous month. I confronted them both and was assured that nothing more had happened than one awkward kiss. I decided to heal and trust my husband again. As we returned to therapy for the gazillionth time (lots of starts and stops over the years because of his inability to follow through) our therapist diagnosed him with ADHD. For the second time. This time he had to face it and began treatment. Just the other day he decided, in his new found honesty, to tell me that the affair had gone on longer, was indeed sexual, and that he had had sex in our bed with our children in the next room, in our son's room, on our dining room table, and other less vicious, but still incredibly painful locations. The affair only ended because I had confronted him about a suspicious text 7 months ago. He met her the following day and told her that it was over and that he loved me and wanted to work things out. When I confronted her 7 months ago she threw him under the bus and stuck to the story that nothing physical had happened, that they had only tried to make each other feel good in their sad marriages.

I am devastated. The person I loved most, and whom I stood by despite all the neglect and pain of 27 years with an undiagnosed partner, violated the sanctity of our home, our children's rooms, our bed, and lied about it after being confronted. Swore thousands of times on his children's lives. Told me repeatedly that I was crazy. He used our children to have access to her. He used our children to manipulate me into supporting his spending time with her and our children while I worked. He used our children to guilt me into forgiving him when I only knew the most phoney version of the truth.  

For the last 10 days he has been taking meds and is truly different in his thought and expression. He says and does what I have needed from him for 27 years. He is wracked with pain and guilt. He says he is committed to me and will wait for me forever. I fluctuate between wanting to hold one another and re-commit to a new life, and wanting to rip his face off and take the kids somewhere far far away forever. I try to hurt him by talking about the fact that this pain makes me feel capable of doing anything and that I want him to feel, not just fear, the pain of me doing the same to him. 

I am from a dysfunctional, abusive, alcoholic upbringing and betrayal and abandonment are my biggest fears; and my love for my children and need to keep them safe and protected by loving parents in a loving home has been the most important thing in my life. He could not have hurt me more if he had calculated the most destructive way to break my heart and soul.  I am so hurt and confused. 

Please help me understand the role of ADHD in his behavior and choices. He is such a good man and despite the chaos and marital problems we have lived through with undiagnosed ADHD, he has been my best friend and an incredible father. We had a great life full of love, travel, good jobs, happy friends - all of our needs were met, except for with one another. This affair makes me feel like that was all a lie and that this selfish horrible person is who he really is. 

Any help, advice or support would mean so much. I'm so relieved to have found this group. I have the book, but because of my anxiety and depression don't have the attention span or retention to read it. I try bits and pieces but I can't swallow enough to really help.

Thanks so much.