It's part of the withdrawal, after the horrible pain and physical symptoms begin to subside...the mental crap kicks in. I feel similarly right now, and tired, so very tired.
Try to stay supportive, don't ask for much in the way of reassurances because it's all an addict can do just to stay off the junk.
There is very little you can do. The only choices you can make are for yourself, not for him. You can not make him want to stay, or get clean. An addict's drive to use is often much stronger than any relationship: lover, wife, even child. You must decide for yourself if you are willing to be a third party in that relationship, because that is what you and your children will always be. Unless he completely commits to sobriety and to your family, that will be the sad story.
I am so very sorry to be so blunt, but it is too often that the opiate comes out the winner. You must take care of yourself first and foremost. Good luck to you.