If your animal companions enjoy marijuana then you should give it to them. If your dog likes pot then give him some, I'd recomend blowing hits towards his face from 3-4 feet away, and blowing very, very slowly so that he gets a small stream of smoke instead of a giant cloud of pain. There's absolutly nothing wrong with getting animals high if they enjoy it, which many do. In fact, I've never met a dog that didn't enjoy pot, and I've only met a few cats that didn't enjoy it, given the right environment.
That being said, if your dog is suffering a lot then it might be time to have him put down. I had to have the same thing happen to one of my dogs a few months ago, it's painfull but it's important to remember that their feelings are what's important. My dog liked pot, so I got her high a few times during her last few days. The pot seemed to lessen her suffering quite a bit and she very clearly had a good reaction towards it. It really can help. Sorry about your loss, it's always hard losing an animal that you love.