I really don't know about the length of time to grieve. How did he handle grief in other situations?
Please don't get too down about the grief. Try to remember that he is not so much grieving the loss of her (yuck) but over himself, his life, and what he has made of it.
I would try to make sure that your D can take your S for the weekend. Why not be a little deceptive and tell everyone that you and H are going out of town but instead stay home for the whole weekend? Get some steaks and beer....and relax!
