If you are telling D about separation I would not allow it be said that this reflects a decision taken by both of you. Don't criticise W's decision.SSay you except and respect her decision. Michele has a video on the net where she explains that better, or maybe it is in her quotes on this forum.
The most important thing is to reassure D that she us and will be loved by both of ye regardless of what happens.
Good luck .
As for your birthday I think not doing something with W will send a better message than spending the weekend with her. Sandi outlines this well in her reply. You can always stick with thevpkan but just you and D. That gives you more time to decide what you want.
You need to decide what you really want to do for your birthday. And DO it. If that us a night out with your mates. Going to a match or concert.This can be as well as weekend with D that W organised or instead of.
Best wishes
R 25 years M 14 years S11 & S13 Working on it alone since Oct 2014 M in trouble a lot earlier (~2 years) Feb 2016. 1st R chat in a yr. Next R chat Aug'17 Still together