My experience, and I've posted this before, it was pointed out to me by more than one member here, the relationship was more of an addiction than anything else.
She had her doc, I had mine-her.
Like alcoholism, the only effective treatment is complete abstinence.
For codependency it would be no contact. Period.
Difficult, yes, but it can be done.
And the fairest thing to do for him also. When you tell him that you want to talk about the 'relationship', he's not thinking that you want to end it, he's thinking that you want to keep it going.