Firstly, I'm very sorry to hear about your dog. Secondly, I know VERY WELL how you feel about how you treated him or thought things. I, too, had very similar thoughts with my dog.

The guilt didn't hit me until the day I had to put him down, and the floodgates of emotion just poured out and I will admit that the grief has been one of the hardest thing I've had to deal with. I often wished to be out of the "contract" I felt I was with him, how he tested my patience to the limit on a very regular basis. But at the end of the day, I loved him very much and while I still get teary eyed thinking about him (it's been 10 months!) I do remember the good times we had.

If you're anything like me, you'll beat yourself up with the should'ves, could'ves, and the would'ves. But, unlike me, you have the opportunity to make the time he has left special. So give him all the belly rubs, treats, and snuggles he wants. Hugs to you.