I don’t think you should assume the death of your hopes, but of your immediate solution to his addiction. His former wife has apparently turned things around and so can he if and when he chooses. He can have an amazing and productive life in Recovery. So many former drinkers have and do, but many have to hit whatever their bottom is and find their way back or not.
The advice above to decide what you want to live with is your next step. I also think having a soft landing is perpetuated the problem, but I totally understand he is your son and you love him and you wanted to help him get back on his feet after seperation. But you can’t quit drinking for him, or control his doing it for himself. Yes, bad things can happen if you kick him out, but bad things are already happening and this is destroying your peace and happiness as a couple and family.
I think I would simply and with love tell him it isn’t working out, you are no longer willing to hear his excuses and support his drinking, and formally serve him an eviction notice—he may not have to leave without it, and even with it will have 30 days in most states—to show him you mean business. The intervention didn’t work because he wasn’t ready, and still might not be. I would just ask him to leave with no compromise or additional promises.
You can love him from afar and get your life back, and hopefully he will choose to get his life back as well. As an adult, this is his decision, and you need to find some kind of acceptance for that as all love in the world won’t stop an addict from engaging in their addiction until they are ready. For some, rock bottom / extreme discomfort is what it takes, if they choose it at all. I grew up with an alcoholic mother, became one myself, and my spouse currently is battling drinking issues himself. I chose Recovery, and so far, neither he or my mother have—she died still a drinker, and he is slowly killing himself with drinking-related health issues. I have enabling issues myself to face.
If we could love and support them well, we would, and this list wouldn’t exist.
I am so sorry for the terrible pain you are experiencing, and I truly wish all of you healing and peace.