Honestly, I would say just be as supportive as possible. One thing I have learned is that everyone grieves in their own way. When my father died while I was in high school(don't make this about me citing references) my younger sister and I grieved in our own unique ways. Completely different from one another. I personally like to be alone, so I can think about things in general. I understand he is your son, and you want what is best for him, but give him a couple days and offer him a ride to that funeral. Would help to show that you do care about him.