Is it fair to leave your A so that they must find recovery on their own?
I believe that is is fair.
They need to be responsible for thier own addictions, recovery, etc.
If needing your support is the reason they can't do it on their own, I'd have to wonder if they were only trying to become sober for you.
Yes, they need support. however, they should be able to find that support in AA. And it's not your fault they no longer have their friends. It's probably that the only friends they have left are the ones that drink!
Can he do it alone?
I believe that is up to each individual. But I'd like to believe that if the A wanted it bad enough, they wouldn't need a spouse to stay and support them.
On a side note, though you didn't really ask.....I have to ask you something. (looking at it a different way). Would you want a spouse to stay with you that was staying out of guilt and wasn't in love with you anymore? Is that fair?
His recovery or not - do you want to save the marriage or do you just feel that it's over?