I am so, so sorry. I have lost three kitties in my adult lifetime - each was horrible. One died of a heart condition in my arms on the way to the vet. One we had to euthanize because he was old and had multiple ailments, and his quality of life had finally evaporated. One (last year, I think I posted about it) had an aggressive tumor that surgery couldn't remove, we had to euthanize him when there was nothing more we could do and it was clear he was in pain. I cried for days each time. All three (well, the ashes of the first two) are now buried under new gingko trees at our farm. I still talk to them when I pass those trees.
I'm generally not a sentimental person and don't really believe in an afterlife, but the poem The Rainbow Bridge has always given me some comfort. I hope it helps you.
The Rainbow Bridge
inspired by a Norse legend
By the edge of a woods, at the foot of a hill,
Is a lush, green meadow where time stands still.
Where the friends of man and woman do run,
When their time on earth is over and done.
For here, between this world and the next,
Is a place where each beloved creature finds rest.
On this golden land, they wait and they play,
Till the Rainbow Bridge they cross over one day.
No more do they suffer, in pain or in sadness,
For here they are whole, their lives filled with gladness.
Their limbs are restored, their health renewed,
Their bodies have healed, with strength imbued.
They romp through the grass, without even a care,
Until one day they start, and sniff at the air.
All ears prick forward, eyes dart front and back,
Then all of a sudden, one breaks from the pack.
For just at that instant, their eyes have met;
Together again, both person and pet.
So they run to each other, these friends from long past,
The time of their parting is over at last.
The sadness they felt while they were apart,
Has turned into joy once more in each heart.
They embrace with a love that will last forever,
And then, side-by-side, they cross over… together.