My friend’s dog is lost, how can I comfort him?

I have raised a puppy for such a long time. Now I lose it. It will inevitably make me very sad. My boyfriend used to have a dog at home. He has a very deep relationship. When he lost it, he cried so much... This It's useless to persuade people to do this, because after all, people have feelings. You can only slowly dilute this emotion as time goes by..