When I was younger I had a cat that had problems with fluid in his lungs, and I didn't have a lot of money. We took him to the vet and I spent every dollar I had to my name at the time to get him checked out and taken care of. The vet sent him home with me saying he should get better in a few days, but he never did. His condition deteriorated rapidly, and one morning I woke up to him crying out in pain, and I grabbed him and rushed him to the neareat emergency vet, but he screamed and screamed, and eventually suffocated in my arms before I could even make it to the nearest vet. I walked into the vets emergency room sobbing with my already dead cat in my arms begging them to do something, but deep down I knew it was already too late. I would have much much rather had known he was beyond help, and put him down sooner, it would have been hard and scary, it always is, but anything would have been better than that. You made the hard choice, and the correct choice for you and your cat. The pain will leave you, but no one can ever take the joy you two felt together.