How much did my cat suffer?

For the last few weeks my 16 year old maine coon's stomach was getting fatter and fatter while at the same time he was getting skinnier and skinnier (if that makes sense). We thought it was worms but after checking his stools we found none, so I umed he was just becoming a fat cat because he was eating so much. Than he quit paying attention to food, and quit wanting to use his litterbox, quit wanting to hang around in his usual spots around us. All he did was hobble around (his hind legs werent working so well by this point), and hide in weird spots beneath the pc desk and stuff. We finally took him to the vet yesterday because he wasnt responding to noise and was acting almost in a trance. The vet instantly recognized his status as the final few hours of a stomach tumor caused by stomach cancer, in which his stomach was filling up with fluids. He said we SHOULD put him down but I wanted him to die at home with us in an enviornment he knew around people he loved, instead of in some damn veternarian hospital. The doctor said it was too late to operate. He said even if we had brought him in weeks ago he was still just TOO old to successfully operate on. The doctor said that he would either go peacefully from a heart attack or his lungs would fill up with fluid. After 2 hours of watching Jacko wind down in my den, he started breathing heavier and heavier, shorter and shorter breaths. He started howling and looking at me almost like he was expecting me to save him. I felt powerless and sad as we watched him 'suffer', or as it seemed. How much did he suffer. It took a LONG time.