It's fairly textbook, he clears up just a single sysmtom and not the actual cause. And the cuase will out even if one sysmtom is denied.
I'm not a "doctor", more like... have been a fellow sufferer of what ails you.
It is so much easier when you have The Map with all the landmines, pitfalls, boobytraps, treasure and power-ups all marked out on it. However you only get the perfect map for you...once you've done the walk. Cos you write a bit more of it after you just walked or staggered through a bit of it.
Which is entirely the wrong way around in terms of usefulness. 
But, those of us with our laminated maps don't want to leave you wandering along blindfold if a glimpse at the maps we had to write might help.
Not one of us will tell the walk (stagger, stumble, fall,over, get back up again) was anything like easy. But then again all of us would tell you it was worth every bruise, sprain, fracture and blinding flash of pure pain along the way.
Your husband won't want or need to address the cause rather than the sysmtom while you are still there to be blamed as the "cause by proxy". I can't promise you he will ever address the cause. For his sake, your son's sake, I hope he does, and honors what it cost you to get him this shot at seeing the need to make real, rather tha token change. But that will be up to him. Just as it has always been.
He has a long, hard road ahead, even if really successful, really quickly he'll have several years of work before he will be "safe to love" again. But you are giving him his absolutely best shot and saving your son from inheriting his father's damage in the process.
Nobody can ask more of you than that. Not even you, your harshest critic.
You haven't just tried to fix things and make them work. By taking this step, you are fixing things and making them work. It doesn't end up in the confguration you wanted, but it will end up in the confguration that is needed. By being apart you are giving every single person concerned their best opportunity of avoiding the harsh future being written by month after month of staying together, all three of you trapped in a cycle created very very many decades ago.
We are taught almost exclusively that love is holding on. The truth is, love is also definitively letting go ... when the alternative is destructive for all concerned.