I recently lost my oldest brother(51) to brain cancer...very unexpected. That was in Feb. Three weeks ago I lost my only niece (18) to a car accident. I am trying to give you some advice from "the cave".
With sudden family loss, each person is individualized. The whole family dynamic changes. No other family member or friend, or loved one can truly put themselves in the cave with the person dealing with the loss. Even with a hundred people mourning along side, its still a very lonely place.
I dont think your b/f can feel much beyond his pain right now. But, knowing you are there, loving him, even if silently, surely means the world to him.
Expect happiness and sadness and anger to come in spurts and please try to understand. Everyone mourns differently. As hard as this is for you, especially during your own mourning process, try to stand by him.
If I can offer any other insight to the cave, let me know. Im living in my own cave in hell right now and will gladly share any advice you ask for .