Ferbie --
Here's an official, patented MB ((((((Hug)))))) just for you!
It certainly sounds as though you've been carrying the burden of your marriage all by yourself for quite some time now, at least since last fall. H's actions and continued poor choices do indeed make it very hard on you and your family.
You need to hang in there for yourself and for all of your children. You've been doing a great job so far, a wonderful job, as the responsibility for your family's stability continues to rest almost solely on your shoulders. Whether or not things change between you and H, that dynamic may still be in place. In other words, you've got to think about you and children first for now. How can you provide maximum protection and stability for all of you? What can all of you do with this set of circumstances to help you grow and learn and heal? Be proactive and not solely reactive!
I know you miss him and your Step-D's, but you don't miss the tension and stress that H's proximity brings. A book I'm reading says, "Don't waste your pain." Situations like this hurt everyone, even your H, who doesn't even realize that. Try to focus on what you have and not on what you don't have...for now (hard to do, I know, but perhaps necessary for survival), and realize that the situation is temporary, that your life will not always be this way.
I'm sorry for this in your life, sorry for your intense pain, sorry for this immense disruption. Richard Bach says that "every problem comes to us with a gift in its hands." What could possibly be the gift here...?
Ammon