I feel your pain I have put 2 animals to sleep so far and each time it gets harder and harder for me to deal with. the last one I put down was my baby he followed me everywehre and slept on my pillow next to my head at night and just purred away and boy do I miss him. he wasn't even 7 when I had to put him to sleep but something was attacking his red bloodcells and that caused him to stop eating we tried everything to get him to eat again and nothing worked
and I didn't want him to starve to death so I took him and had him put down
. My other cat was 12 and had diabetis and kept having diabetic seizures and after catching him having one that day i took him to the vet and had him put down (the meds just weren't working and we tried switching them so many times in the 2yrs after he was diagnosed). I still to this date sit here and think about both of them and how much i miss them. the pain will get easier to deal with as the days go on but the cat will always have a place in your heart.