I think this is what's best..."You need to know that things between your mom and I aren't getting better. I know that I told you that my dad was going to pay to send you to (school she wants to go to) but I don't think that can happen now. Your mom doesn't think it's as important as in the past, before high school and we just can't afford it now. [You cannot speak for your W. I wouldn't bring it up here to make her the bad guy in this. ]Your mom now wants to not only leave here and live somewhere else, she also wants to end our marriage. [Why are you going into too much detail here? Does D really need to know this info??]This doesn't mean she doesn't love you, it's not about you but about her and I. We both want what's best for you and may not always agree on what that is but I can tell you I will always take what you want into account. You will always be my daughter and I will always be a part of your life, you mean the world to me and that will never change. Things are going to be very different and we don't know yet what is going to happen, where your mom will live, where you will live [Yikes! That will terrify D in stating that you don't know where she'll live. Why would you say that to her??], how you will stay a part of both my and your mom's life. I know it's hard not knowing and I would have moved heaven and earth not to have to put you through this but sometimes there is just nothing that can be done to stop bad things from happening. [It does sound heavy and imagine how heavy D would feel hearing this line??]For now just know that I'm here and if you have any questions or want to talk I'm always available and I promise to always tell you the truth as best as I know it." [Huh? It seems to me that you're trying to present yourself as the choir boy and W as the she-Devil when it comes to "truth" telling. That is ho it came off to me in reading that comment.]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You'd want to rethink those comments and try to think how D would feel with this type of news. You would want to keep it simple to the bare facts, that their mom is on a journey that people may not understand at all, and that you are sad about this.
