First of all, Welcome to Pet Talk! Im very sorry about your cocker spaniel.... I think like many pet talkers here will say...your pet will tell you when its time. It is a very difficult decison to make. You might never be ready to let him go, but he will be at Rainbow Bridge, and no suffering. I had to put my 6 year old Dachshund down, due to a spinal injury...I wasnt ready, but I knew it was time...Im sure the 5 years you had him for were the best years ever, and he thanks you for them. Best of luck to you and your dog.