So hard, they each have personalities and their absence makes such a big hole where they used to be. I have missed him sleeping on my chest, it just isn't the same. He's in a better place now with no pain, so for that I am grateful. He lives on in my memory and heart.
I'm sorry you've also had to experience it, a feeling I dread with having such close companions but the pain is worth all the time we get to spend with them when they're with us.
Hugs
You described it perfectly because they are always present in our mind and heart, I remember them every day, but I know they are better, a big hug for you, from me and my seven cats.