Cried in vets watching her pass on my knee with the death fluid flowing through a clear tube from an injection 20 feet away. Hard. Not been able to get another cat since. One day.
I swear my cat could understand human speech, and would innocently climb up your leg if there some chance of curry to be had. I nursed him, hand feeding him sometimes, for a year before he just about gave up eating. I had the vet come to the house, and my friend was euthanised while he was cradled in my lap. It was a shock to me how quickly he went limp. My wailing should have embarrassed me, but it didn't. I was just about as distraught as I've ever been. That was nudging on 20 years ago, and the thought of that moment still upsets me.
Like you I swore I'd never have another cat. Fate had other ideas. A relative worked at a vets, and a kitten had been brought in with suspected cat flu, a kitten that would be homed by the vet in time. It was suggested we look after the kitten for a week to make sure the vaccines worked and the kitten could rejoin some others passed to the vet for homing.
It was a dirty trick because the cat took to me very quickly. It followed me everywhere, and wanted to watch everything I did. I have pictures somewhere, of it watching me paint a wall.... If I opened up a floor void, the kitten had to go inside to look to see where it went. On day 6 of the 7 day foster period, everyone in the house knew it wasn't going anywhere.
That was about 11 years ago. What is now a 5kg bag of fluff still follows me everywhere in the house. When I come in late in the day, it doesn't matter where he is (asleep usually) he'll come down the stairs to greet me. He is treated like royalty, with it hard to imagine him having a better life, he's also brought us and me in particular, a great deal of joy.
Was it a mistake to let the kitten come here? Not for the cat. He'd already had an unpleasant start to life before he arrived, and even now, he's scared of ANY sudden noises. He has the run of the whole house, and the doors he can't open, he knows if he sits next to the closed door and meows for long enough, that door is going to get opened. Mistake for us? I sometimes think so when there's a fur-ball and his regurgitated last meal to clear up, but that thought lasts for about a minute. That thought lasted a little longer, when one of the two rats he's brought home, was still alive when he dropped it on the kitchen floor.....
That was a bit traumatic. On balance I would say he's been a rewarding experience. If he goes before I do, I've possibly a thousand images/videos of him to reminisce over. If I go before him, he'll just have to wake someone else up in the early hours, for some fuss and a cuddle.
I'm not sure we're supposed to only have one close deline friend our whole life, and there's certainly plenty of them looking to be a close friend....