First Michelle, learn the 3 C's. You didn't Cause it, can't Cure it, and can't Control it. He's an alcoholic. Sadly, although we all want to step in and "help" our A's...there is NOTHING we can do about their choice to drink or get sober. The worst thing we do is get involved trying to get them sober and ultimately enable their addiction.
I agree with dandylion. Sounds like in his attempt to not drink for a day, he is experiencing physical withdrawals. That tells me he's drinking more than you think he is, and he now has a physical dependency. He needs medical help, detox, to get through that safely. He can check with his health insurance for detox services, or go to an ER. But HE has to do those things....don't make the mistake of doing it for him.
IF he commits to sobriety, he has a long road ahead of him. Take a long hard look at what you're signing up for here. Read the sticky's at the top of this page, and read these posts. There are red flags all over this thing. You're ex cheated, well the A cheats as well...with their drug of choice. They will lie, manipulate, cajole etc to keep their addiction going. He already lied to you about working on his marriage. You don't know the truth behind their break up, it's likely she dealt with this as well.
What can you do to help him? You may not understand what I'm about to say, but stay on here and you will eventually. If you want to help him....get out of his way. Don't throw yourself into this situation, it doesn't help. If he wants sobriety, it's important that he do the work to get there. He needs to experience the consequences of his choices, don't step in to soften things.
Most importantly, take care of YOUR health. You don't want to bail on him...don't bail on you. Get to Alanon, and get educated about what you're up against. If you do choose to stay...you need to know what you're up against in life as you move forward.
I'm sorry if this sounds harsh, that's not my intention. But it doesn't help you to sugar coat this thing.