My condolences are offered as well. I lost my two original cats a few years ago, one was 22 and the other 24 years old. I didn't have the courage to put them down, I just couldn't do it. I commend you for having the courage to do it. There is no pain like losing best friends of so many years. The pain subsides, but never really goes away completely. I have two new cats now, and they are not the same, but they are good friends too. After a time, I hope you get a new dog. It will help.
Rick