When I got my first cat he was already old and well, he got much older and then he got sick and I had to euthanize him. I was heartbroken when I lost him, but I also felt guilty about this decision since I could not afford to keep him. I had a dream about him some time after, that I was in the world of the dead with him and it was a wonderful place: warm, bright blue skies, the sun was very bright, almost blinding me, there were green plains and trees in the background, colorful flowers. My cat was there playing with the flowers, and we played together, he seemed to be very happy and I felt he wanted to tell me that he was in a great place now without suffering and that I should not worry about him.
I just want to say that I'm sure that your cat is there now, relieved, happy, and playing in the fields. I hope that my message will calm your pain a bit.