In fact, when we lose something that is very dear to us, the pain is much deeper, especially if it is your pet that is your companion, pets are usually very favourite of every people, we spend time with them occasionally. But there comes a time when they leave us alone, that time is very emotional for us.
Personally, I also have a pet, but it is not a dog, but a cat. It is my favorite, when I am at home, the cat comes to me most of the time, my cat loves me very much, I also take my cat for a walk occasionally, I love my cat very much.
This is my cat:

Now the situation you are in, at the moment we can only console you, nothing more than that, your Little Nismo was much more Emotional to look at, and much more beautiful and cute, if I had also lost such a dog, I might not have been able to live very well.
But brother, my condolences to you, the love and joy that Nismo brought to your life will live on in your memory forever, but you should start raising another dog, and love him like Nismo, you may not get Nismo back, but you will definitely get a
second Nismo.
The difference between Dogs and Cats is the Dog will mourn you when you die, the cat will eat you.