well, SadHub, it sounds like you've had some incredible personal development over the last few days. All of those difficult things going on, and yet you still said that you had a wonderful weekend. That speaks volumes about how far you've come.
I know that you feel badly that the relationship between D17 and your W is deteriorating, but I hope that you will try not to internalize that too much. That is their relationship, not yours. Your D17 is trying to set her own boundaries right now and she is old enough to do so. I think that she can also see that it is your W's circus. She is a pretty remarkable kid who has a lot of clarity on the situation.
All you can do is support D17 and encourage and help her to develop her own support system to deal with the many changes in her own life (GP, therapists, friends, family, etc.). Make sure that she has her own therapist to talk to and to help her sort things out. Unfortunately, you are too close to the situation, emotionally, to offer D17 the impartial perspective she really needs right now on her relationship with her mother. Make sure she has the professional help she needs to help her with that.
I just got out of my own therapist appointment, and I am now wishing that I had seen one earlier in my life. It might have helped me deal with my current situation in a healthier manner. Would have, could have, should have...
I'll check in on you later. I hope that you are doing well today. Pencil smiles!!!
H: 44, Me: 45 Married: 20 y Together: 25 y no kids Walk away: 12/15 Asked for temp separation 12/25/15 PA confirmed 3/16 (apparently neither the first, nor the last PA he has had) H filed for D 5/16