I'm sure you and your dog enjoyed each others' company to the fullest before it was time to say goodbye. And if so, is there really so much to feel bad about? :)

I was a caretaker for my mom while she had terminal cancer and this is what I have to always go back to. I feel guilt about so many little things I could've done different, but she never felt bad about them so why should I continue to emotionally hurt myself over them? I feel the guilt, cry it out so I'm not emotionally constipated, then think logically about it and always go back to how much fun we had in the time I was there for her.

You're just so right about it all, but like anything worth anything in life, it's hard to do but we all keep working at it.