Also sorry to hear of your loss. I don;t think you ever forget them or get over it, just kind of get used to living with the loss.
We had two dogs the same age as eachother - a staffie and a bull terrier, and sadly, staffie died aged 6 (brain tumour). It was all very sudden - he fell ill on xmas day and we had to take him to the vet's the first day they opened after xmas. We had him put to sleep the following day and the worst thing was, he was still quite lively and looked in the peak of physical health - muscly, good size, really shiny coat. Even the vet commented how fit he looked. It was awful waking up that day knowing we had to take him to put him to sleep, and I took him for a last walk. He was suddenly very ill during the walk and although he looked ok, he looked very unhappy and under the weather. He played with the neighbour's dog in the garden then we took him to be put to sleep, as the vet said there was nothing she could do and he would start to get very ill.
We decided to bring him home and bury him in the garden. Although Mr H was reluctant at first he realised we had done the right thing soon after. We'd got Harry on my son's birthday and my son is autistic - the dog had been his life, basically. We planted an apple tree over him and to this day when my son goes out anywhere, he always goes to 'Say hello to Harry' at the tree, first. Sometimes he just says he's going out to 'check Harry'.
The grave gave us a place to focus and my son did come to terms with it. He also gave a donation to a staffie rescue charity in the days after Harry died and that gave him something positive to focus on.
Our surviving dog is now 10. I think of Harry every day though as he used to run upstairs, wake me up by standing on me, then sit at the end of the bed looking out the window. So every single morning, 4 years on even, we wake and he's not there and we miss him. But it gets easier.
We lost another staffie years ago, aged 6 too. (Also cancer). We have her photo in a frame in the living room alongside all the family pics, and never forget her, and still talk about her.
You could plant a tree in Casey's memory. My son finds it really helpful, visiting the little apple tree.