I think it'll do you good to stop thinking about it from RAH's POV & think about it from DS's perspective. Instead of worrying how RAH is going to take the news, worry what will happen with DS's entire future if he doesn't get the help he needs. He has ONE childhood. He didn't make a single decision that created the need for therapy, none of this is DS's doing.
I had to stop thinking of it in terms of swimming away from RAH while he (chose to) drown & think of it in terms of swimming toward my DD, standing on the shore. He was an adult living with his own decisions, she was a child with one chance for a decent childhood.
Remember that just being sober alone isn't enough to create change - the secret-keeping is just another way he's choosing to drown, do you see that?