Which battle to pick first?

I am new to the forum, and the ADHD diagnosis is new to my husband. The conversation began for us in earnest 2 years ago, when his defenses were down and I took the opportunity to suggest he might have a learning disability. He admitted he had also wondered if he might have an LD, and said he'd like to be tested. The results indicated that he didn't have an LD, but revealed a primary diagnosis of clinical depression and secondary ADHD. After a year of consistently taking Lexapro, the depression symptoms seemed to have lessened significantly, but our marriage was suffering more than ever (we also have 2 boys, age 2 1/2 and 14 mos.). Psychotherapy began inconsistently about 5  months ago. He liked his therapist, which was a bonus, but I was at my wit's end and feeling some depressive symptoms myself. I met with his therapist twice, 6 weeks ago, and then we all met about 3 weeks ago. The therapist felt strongly that my husband's primary diagnosis was ADHD, and after listening and reading more, it was as though I was reading the story of what I'd heard about his childhood, and the story of our relationship. It fit us and him to a tee.

His therapist recommended that we first tackle the ADHD, and secondarily our marital conflicts. It seemed to make sense, but then a week ago I uncovered a bomb: my husband has been having an affair for the last year and a half. He ended it immediately, and is remorseful, ashamed, and I do believe has hit the proverbial rock-bottom. I waft between rage and mistrust to wondering how we now determine if we are fixable. We have somehow managed to get through the last week until our therapy session tomorrow morning (our therapist was out of town -- otherwise we would have tried earlier). 

My husband has been a very different person since I discovered the affair -- different for the positive, in general, and is genuinely trying to see and edit his behavior. But my question is this: what do we try to fix first? His ADHD? Our ADHD marriage? Our marital breakdown? The fear we both have that our children will display characteristics of ADHD? I see, and he is starting to see, how pervasive this really is. At this point, I do want to try to save our marriage, but I am so overwhelmed in what the first step ought to be. Thoughts?