I'm sorry for your loss.
I took my beloved cat to the vet after I found her listless and foaming at the mouth. It took just over 24 hours for the vet to ring me to tell me she'd drunk anti-freeze (highly dangerous and they love it).
I was a new customer but he obviously sensed the connection better than I did and called me and asked me to come and say goodbye to her. I did.
It was only afterwards that I realised that in a lifetime of owning cats, she had been the "one" and to this day, three years later, I still mourn her as I would a family member.
My new vet was amazing through that time and it made all the difference.
While I'm at it, if you haven't much money, I can't recommend that tenner a month on pet insurance highly enough. It all happened so fast we didn't wait for clearance, we just treated her and if I had to pay it would have cost me in excess of £2000.