Talking with DH about his ADD

My DH was diagnosed with ADD in college, but to be honest, I didn't take it very seriously for many years. I started reading about it a year ago and have recently checked a bunch of books out of the library and started doing more research because I realize that I need to be educated about his ADD. Honestly, his coping mechanisms were really good and worked well for a long, long time without treatment. But finally, the stresses of work and kids and money and health crises have taken their toll and his mechanisms aren't working anymore. About a year ago, he was diagnosed with depression, anxiety, PTSD and has substance dependency issues. 

I have let him handle things on his own for the last year, but it's not working for me. The more I read about ADHD/ADD the more worried I get. However, he refuses to talk about it. He saw a therapist of some sort last year, but wouldn't talk to me about his treatment, other than the additional diagnoses. He's not seeing the counselor anymore. Bringing up the topic of ADD causes him tons of anxiety. I think he's always felt defective and the fact that I blew it off for so many years has made him reluctant to share anything with me. I think he's also a little embarrassed because he had to be the strong one for a long time and there's a few areas he really made a mess of. We're just starting to clean up those messes and it's not going to be pretty for a long time. 

I want him to feel safe and I don't want to nag, but it's not like this is going to get better. We've been married for almost 13 years and have three kids. Our life is not going to get easier any time soon and we need to be on the same team. How do I get him to talk without turning into Miss Nagging? The thing is, I need to feel safe too and right now, I don't. I mean, I'm physically safe, but emotionally, not so much. It's been a weird year.