We had to put my old cat down about two weeks ago. He was a foundling as a kitten way back from when my wife and I first started dating - she found him while working outside, took him to a vet and gave him to me. That little furball then stayed with us as we got married, moved to Yukon and back, and had three kids. All the while being the cuddliest cat I've ever known.
I still miss that old, orange tabby. 18 years just caught up to him, he stopped eating, lost so much weight, and by the end couldn't hardly walk and we had to put him to sleep.