I want to process my thoughts out loud

Cutting to the chase: One month ago I found this book and it scared me with how much it matched my marriage. My wife read it as well.
Overall, our three month journey of going to counseling together and separately has been very good. However, one of the most painful things she has told me is that she feels like I'm her best friend but she's not my best friend. Essentially, she processes outwardly and tells me everything she thinks about, while I process inwardly, which makes her feel less important to me. A big problem my wife still has with me is that she can tell when something is bothering me. Often before even I know. Historically when she would ask what's wrong with me I would reply with "no." I've since learned that I should've said "I'm still processing and I'm not ready to talk about it now." But I'm still having such a difficult time expressing my feelings. Old pieces of wisdom such as "don't begin a conversation while angry" and "pick your battles" make me second guess whether I should tell my wife what's bothering me the moment she asks, due to the possibility of hurting her with thoughts that have not been fully processed. Any advise on how to communicate effectively will be highly appreciated.

Background: I'm 31, male. Been married for 9.5 years w/kids. Diagnosed with ADHD at 24. All I knew about ADHD was that it meant a person has difficulty focusing. Medicine helped a lot with focus.

However, the last three months have been hell. My wife said that if I did not meet her needs (have things in common, go out to dinner/bars/concerts weekly etc) then she would not want to continue being married. 
It destroyed me. I was frantic. Not knowing how to fix something that I thought I had been fulfilling for years.