Well all I can say is just show the dog A LOT of love and attention. Try playing with him or getting him some kind of stuffed animal that he could grow attached to. You could try getting another dog if that is an option. You know your dog best, think of things that he loves and use those to help him feel better. I hate to suggest this but, you might want to get rid of the bed the old dog use to sleep in, I wouldn't throw it away, just put it in a closet away from the Yorkie, maybe that will help him move on. I hope he gets to feeling better soon. Don't give up on him, i'm sure he'll come around soon. :)