It may be helpful for you to give him an opportunity to feel his feelings, and give him some space to do so. He is telling you the truth, when he says you don't know how he feels. Grief, is different for each person, and a process to enter into and go through.
I'm sorry this is challenging at this moment, it is very hard not to be able to help the ones we love an care about when they are hurting.

Take good care of yourself, and your husband will appreciate you even more.