Oh no, I am so sorry to hear this.
I know how hard it is. I have had animals my whole life and my dogs are like family, so these times are very hard and sad.
I worked at a vet all through college and every time we had to put a pet down it was hard....every single time, and they werent even mine.
I always got through it by thinking of how happy they had made their families, how much they loved them and how much joy they had brought in their lives and that the only way the family could repay them was to always love them and to do whatever necessary to end their suffering so they would not have pain.
Always remember the smiles and laughs.
So sorry for your loss