So sorry to hear about your cat. We had to put our 10 YO dog to sleep last year after we found out he had cancer. I had had him since the day he was born. Our son was 2 at the time and kept asking where Roscoe was and we told him he was heaven. He never grieved but I made up for it. It was difficult and I still get sad when I think about him or look at pictures. What helped me the most was to get a new dog. I call her my little angel that was sent to me. We rescued her from the humane society and I think all the time how we saved each other. I needed her and she needed me. You might need time to heal, but consider getting a new cat. It will never replace the one you lost but it can help you feel better, at least it did in my case.
And best of luck to you with your surgery tomorrow