Loyal loving pets are one of God's greatest gifts, but He takes them back from us very soon. We are taught lessons to cherish their fleeting short lives.
I'm sorry for your loss. It never gets easy. I've had the highs of pets, and the lows, many times. They give some of the greatest joys, but also greatest sorrows when we lose them. Your caring for him all these years, humane treatment at the end, and memory, is noble.