Saying goodbye to my best friend

I am so beyond sad and in need of some supportive words. My sweet boy Bear is scheduled to be put to sleep at home on Monday afternoon due to old age aggression issues. I got him as a gift when I was 12 years old, and for the past 12 years he has been my sunshine. He has been the best boy I could have ever asked for and I will miss him for the rest of my life. I don’t even know what to do without him.