I responded, "forget the legal issues we're dealing with. Feel free not to respond to this. That's fine. I'm just saying you need to stop what you're doing. You're continually putting her in the middle of adult things. It's wrong. It's bad for her. You are doing her harm by doing this. Please think about it. Please stop. You and me isn't you and her and it isn't me and her. Leave her out of this mess. Please think about it. Please.
Let cooler heads prevail my man. I wish we had a picture of a tall, cool, frosty glass emblazoned with STFU that we could pass around to people at times like this Because it would serve as a great mental image whenever something like this triggers you.
There were times that my kids told me W said something that really triggered me like this, and a few times I banged out a hot little text to her. But in the true spirit of STFU, I deleted them without sending. Then later when I had calmed down, I would mention it to her in person, like "D said that you told her I was being selfish, I don't want you or D to think that I am selfish, let me know what I can do to make this better." A lot of times we would discuss it only to find out it was a misunderstanding or something taken out of context, but other times it led to helpful conversations on how we could both communicate better moving forward.
Your W comes off as very angry and hostile, but much of that may be how she perceives you are treating her (controlling her and using money to one-up her). Try to ease the tension by understanding her position and feelings a little better and sympathizing and being more respectful of her. I know that can be hard to do but try it for a few weeks and see if things don't improve. I'm not talking about recon, but just to make the co-parenting go smoother, which will help your D.
Because it would serve as a great mental image whenever something like this triggers you. 