Anyone else struggle with issues after their pet's passing?

In my case, the issue is that I now feel that we waited too long to decide to euthanize.

We kept hoping for a minor miracle, or that this treatment or that medication would make him get well enough again to go on. (He was a 20-year-old cat with renal insufficiency, possible pancreatitis, possible osteoarthritis and just general old age.)

We only got the kidney insufficiency diagnosis just over a month ago. We bought the prescription foods, took him to see a vet several times, got medications, the whole works. Inevitably he declined pretty dramatically in the last 10 days. I kept hoping he would get better or at least maintain some quality of life. We made tentative appointments for euthanasia but cancelled them when he would have a good day or even a good part of a day. There was always some little ray of hope.

When the time finally came (just 2 days ago) we took him to a different vet than his regular one. The reason was that his regular vet doesn't allow the owner to be in the room with the pet for the final administration of the euthanasia drugs. I feel she was disappointed that she didn't get to see him or evaluate him again. Who knows, she might have been able to treat him and he might have improved.

His last few hours were peaceful and pain-free, thanks to gabapentin, but before that he was in pain. He even ate and drank a little in the car once the gabapentin kicked in. Another little ray of hope! But we ended up going through with it.

I am really struggling with the fact that I allowed it to get to that point, and I did not take action sooner.

Did you have any issues or regrets that happened after the loss of your pet?