We have been dating for twice the time he and his ex went out for, and he still can't get over her. He talks about her and says he wants her in his arms again.. I have helped him get back to being friends with her, but she won't do anything. And he's given up but can't get over her... Help?

There's nothing you can do. It's great that you're being patient and supportive. But it ultimately comes down to him.
A tip for you though, be careful that you're not just the rebound. If he's dating you but not over her, well, that kind of makes it sound like you might be. But, then again, I'm not in your shoes so I could be off on that point.

Justcurious55 is right. Your are obviously his rebound. He's just with you to help himself get over his ex.

It was a really bad idea for you to help him become friends with his ex again. He obviously still has feelings for her and you're just helping him take the first step to try to win her back.

It's time for you to break up with him cause there's no way to trust him. He's still in love with his ex. If you really want to help him, then help him as a friend and not as a girlfriend.

I have to aks, why do you want to be with him when he still talks about wanting to be in his ex's arms again?? That would be a pretty good indication to ME, at least, that perhaps this won't work...