I am sorry that you're feeling down and frantic with the changes. Center yourself and phone your L about your options.
I am realizing just how much I hate being alone all the time!
This tells me that you are not quite comfortable in your own skin. I've been alone for 10 years today (today is the day Ms. Wonka moved out with the OW) and I've been doing just fine thanks to GAL. Yep, it was tough in the beginning. Now? I relish being able to hog the bed sheets all by myself and vaccum the house naked! Yeah...just threw that one in for the shock value.
I need to talk to my D14 about the D.
Matt, you are the adult here and you don't want to put an undue burden on your D14. You can be very matter of fact by stating that you and her mother will be getting a divorce. Although the parents are not able to live together, D14 is very much loved by you and her mother. If D14 brings up the face that her mother is not well or whatever, just state that it is for W to figure out on her own and that you're sad for her. No need to bash or badmouth W here. After all, she is their mother.
You need to be very clear to D14 that she has full access to both parents. You can simply ask her what her preference is in regard to the primary household. Then shut it. Thank her for her thoughts and that you would do your best to work this out. No guarantees.
Then you may need to gently broach the subject of school and let her know that attending the area private school may no longer be an option due to the divorce. This is a good teaching tool for D14 that this is a transition and she needs to learn how to adapt to this change.
I don't want you to bring up W in this and telling D14 that she cannot go to private school because of W. Shut it. Just state that it is the reality with the changes from W moving out and proceeding with the divorce. Yep, it [censored] for you and D14.
You all need to adjust to a new normal going forward.
And yes! Talk with your L first before you have the convo with D14.
Yeah...just threw that one in for the shock value. 
