He needs to step up to the plate and get her out. I ask you this though, you say he's a good man, is he really when he's sacrificing your relationship because he hasn't got the backbone to get rid of her? If there are no legal obligations to keep her around, I say it's ON HIM. We already know she isn't a great person and is clearly manipulative but it really is NOT on YOU to do anything about this. This is his burden - and I'll be honest, outside of legal obligation to let her stay, he has no excuses.

Honestly you need to let this guy go and let him deal with it. Tell him when he's let go of his ex and stopped being led around by the nose by her, he can talk to you then. Depending on how he reacts to your departure, it will speak volumes as to how much he actually values your relationship.