This was included in one of the sympathy cards my Mom received:
Nothing can make up for the absence of someone we love and it would be wrong to try to find a a substitute. We must simply hold out and see it through. That sounds very hard at first but at the same time it is a great consolation for the gap, as long as it remains unfilled, preserves the bond between us. It is nonsense to say that God fills the gap. God does not fill it but on the contrary keeps it empty and so helps us to keep alive our former communion with each other even at the cost of pain.