I'm so sorry for you.
You were NO DOUBT the best thing that ever happened to sweet Coco. You made her life safe, loving and peaceful.
I have had to make this same difficult decision in my life. And I have gone through the same replays in my mind for days and weeks after. It's so difficult.
The only thing that makes it better is time.
I do believe that our pets go on to heaven. I would like to share a story with you. This brought me so much comfort after I had to make this same decision for one of my dogs. I hope you find comfort in this story too.
In November of 2000 I had to put my dog to sleep. She was an American Cocker Spaniel named Molly. I had her since she was 8 weeks old. She was almost 16 when I made that difficult decision. She was suffering. She had cancer as well as many other health problems.
My grandfather died in May of 2001.
My husband (ex-now) was cheating at the time. So this was a very, very difficult time in my life.
Prior to my grandfather passing away, he was staying at a care facility. My youngest sister lived a short distance from this facility. She and her daughter would go and see my grandpa on a regular basis prior to his death. My niece at the time was about 2.
My niece and my grandfather had a close relationship. And she was too young to understand death & dying, etc.
After my grandfather passed away, my sister did not tell my niece. (again, too young to understand) she also was not told about Molly.
My sister began hearing my niece talking in her room at night. One night she went in and my niece was yelling. Not upset yelling, just loud talking/yelling. My sister asked her what was going on. My niece said, "Molly is here and she keeps jumping on my bed!" My sister gently continued the questioning and asked, "How did Molly get here?" And my niece said, "Grandpa Pete brings her to play with me." my sister continued with, "Where is Grandpa Pete?" and my niece pointed at the window and said, "Right there!"
I believe my dogs who have passed are with my grandfather. And for whatever reason, my niece could see them together. When my sister told me that story, it brought me such peace. Molly used to love to jump on beds. But she hadn't been able to do that is such a long time due to her health problems. And knowing that she (and now other dogs) are with my grandfather) waiting for me is so reassuring.
I hope you too find the peace you so deserve for loving so unselfishly.