i really feel for you, that looks like a dog that has a lot of love to give and take... i had a cat that i had since i was like 4 who had diabetes and all sorts of problems. it was a really tough choice, but we figured it would be better if he were put down, out of all the pain he was enduring. i really didn't want to, but we chose to put him asleep, and i think it was probably better for him, even though he was very well loved, and a happy cat, he could barely walk and would soil himself everywhere. i stayed in the room with him when he was being put to sleep, just patting him and making his last moments happy ones. im not telling you that this is what must be done, but it sounds like your dog is in a lot of pain most of the time. i don't want to sound like a dick, but it isn't all about you, if your dog is having trouble continuing with daily activities, maybe it is best to put him to sleep. don't get me wrong, i've had 3 cats and a dog, its never easy to say goodbye to a lifelong friend, but its better to let them go than to see them in pain.

I really feel for you, its always a tough decision...i hope you feel better soon