As someone who has been sober for some time now, several years, I can still remember that one of the most daunting parts of early sobriety is when as you put it, the chemical fog begins to lift and reality starts to come into focus.
Think of alcohol as a thick pair of gloves and life as a rose bush. When you have the gloves on you don't feel the thorns and you don't appreciate the soft beauty of the flowers. When the gloves come off we can feel both and sometimes the fear of the thorns makes us timid to get out amongst the flowers.
The "real world" is much different than a structured environment of rehab or even the haven of AA meetings; morning, noon and night and I have seen and still see folks who literally become AA junkies. What they “might” do becomes their safe place and the actual doing becomes something we talk about and hesitate to put into action.
Most folks need to take a deep breath and let go of the side of the pool and start swimming in the stream of life before they develop confidence in their abilities to function without alcohol. I would venture a "guess" that you may be hearing fear more than fog or God forbid a "wet brain." Time will tell, but hopefully he will use the support outside of rehab that exists in a program like AA. There is no magic in AA, just folks who have done what we are trying to do when we first re-enter the world. AA was my "safe place" when I got jittery about living, however it became increasingly a scheduled stop and not my destination, the longer I stayed sober.
Small victories, growing self-confidence and some friends and family who are supportive of our "attempts" to live a sober life are really the things that allowed me to grow into a life of sober living and over time one that I truly enjoy.
I haven't said anything very insightful, but I hope my experience will give you a glimpse of what the world can look like after we stop looking at it through the bottom of a glass. BTW, when I quit I was 46 years old and was consuming as much as two fifths of Canadian Club a day. That was in 1999.
Best wishes to you, your family and your ex. The pleasure is worth all the pain.
Jon