Thanks for all these thoughtful responses. He went out for "the paper" and spent the afternoon at a pub. Again, he was distraught. He came home almost in tears, saying, "It was like I went mad when I walked by the pub, this voice in my head said, 'What's the harm?' and before I knew it I'd drunk four beers. I want to stop!"
I said, "Let's get your toothbrush. I'll drive you to the rehab place, I'll stay with you there tonight if you want. Go on, get your bag, I'll start the car."
He didn't want to, saying, "It would cost several thousand pounds." I countered that we'd pay more than that on bail or fines when he eventually gets caught for drunk driving.
It turned into quite the scene, me saying, "Just give it a try. We have to do something. I don't want to leave you but I can't go on this way." And him countering, "I can't do it. I don't consent to it. If I just do it just to placate you it'll never work." (Which, he kinda has a point.)
He did agree to call his counselor and ask him what he thought about going to rehab. The counselor wasn't available but might call back.
I was crying but I forced myself to calm down and we held each other and talked. Now he's upstairs, resting, waiting for the pubs to close. He said, "At least now all the shops are closed, thank God, and if I make it to 10 the pubs will close too." (It doesn't help that we're in a real drinker's town!)
So here we are. I still have my apartment in place for the end of the month, haven't told him about it. If things don't change once he's sobered up tomorrow I will leave for a few months. I don't want to divorce him, ever. The apartment is right in town so I could still look after him. What I want is for this burden to just be gone, from both of us.