D13 knows that things are really bad with us. I am trying to be a great dad to her but she is somewhat closed off right now. It's a balancing act of showing her love and giving her space. I am doing all I can to make her feel safe and to show her how to handle a crisis with dignity and respect. It's the strength part that I have been severely lacking to this point.
I know it's hard, man. I had to do it and it about broke my heart, and my girls were 18 and 20 at the time. Let her know that you love her, her MOTHER loves her, and that you still love her mother but that "Mom is just making some bad choices right now" or, alternatively, "Mom and I are just going thru some things that we need to figure out right now" (whichever you are comfortable with). Let her know - -frequently! -- that "this is NOT your fault!", and also tell her "I will always tell you the truth and you can ask me anything."
It's imperative that she have at least one parent she can get the truth from at all times, during this difficult period.
Hang in there, man. You sound like you do have a real clear understanding of the dynamics of it all, and it's only in the "DOING" part that you're having difficulty. I found that praying for STRENGTH, daily, really helped me. I'm a "fixer" and a "pleaser" and a classic "Mr. Nice Guy" by nature, so NONE of this came naturally to me. STILL doesn't! But I had to learn new skills, and I'm proud that I did and they still serve me well and now I can teach them to my adult children to use in THEIR relationships.