You are focusing too much on HIM. You need to focus on you. Don't worry about a D or anything else to do with him. You are letting yourself get worked up again. He is out there having a good time while you are home with the kids. You need to let go. Letting go does not mean file for the D. Letting go means start living for you and the girls.
You are in for a long ride and you need to be prepared. As I was told in the beginning: Hope for the best but prepare for the worst. I don't want you to think I am saying your H will never come home because I am not. Ask yourself, do you want your H to come home while he is in his own world? If he came home right now, he would make your life more miserable.
I think it was a good thing he didn't come by this weekend. You are not ready for it. You would have melted in his hands like chocolate. You need to be stronger before you confront him.
As hard as it is, try to go without thinking of him 24/7. When you stop living your life for the day he comes home then you will start living YOUR life again. You can always hope but not dwell on it.
Today marks 18 months that my H left and he has mentioned the D word quite a few times. He has not done anything about it yet. If they want a D, they would do it as soon as they could. These men don't know what they want. Your situation is a little more complicated since Cassie is involved. I don't have another woman in the picture. I can be thankful for that. Sometimes I feel it would be easier if there was another woman because then I would feel I had someone to compete with.
You are smarter and stronger than you think. A year ago I was the same as you. I thought of my H 24/7 and cried constantly. My life was a living hell. (not that it is 100% great right now) I have learned to live for me again. This separation has made me a stronger person. I have grown from it. I am a better person because of it. As weird as it seems, my H has become a better person and grown from it too.