It's really hard to tell from what you wrote what you are doing when you're going dark- for example, how long have you done it and what have you stopped doing, and so on. It's also hard to tell what you've done when you say you have tried to have more contact with him. When you say things have worked, but only for a while, I'd like to know more about that too. So, in the true DB fashion, what I'm saying here is that you need to be more specific.
But in the meantime, in regards to your children, you need to tell him that even if he decides to be out of your life, he needs to stay in his children's lives. Then be specific with him in terms of the kind of contact you'd like him to have with the kids. Call every night, see them twice a week...get what I mean here?
