We just lost our cat a few months ago; we have had her for almost 16 years as well. I agree with 290Pika... take time to grieve, and then make sure you get back up and get back going. I found it was good to think about the happy times we had with our cat, the strange things she did, memories of her. It really helped us, at least, after we had gotten past the sadness.
Personally I don't feel like animals go away when they die, I always kind of feel like they stay around. I could be crazy for saying that. But hey, they came from the earth, I figure they are still here somehow.
know that you're not alone. I also had a dog which died of cancer. There was nothing we could do.
That's the problem with owning a pet like a dog or cat - you get emotionally attached and then they die (usually) between 8 and 18 years, depending on the animal and breed. Your dog was 16-17 years old. She lived a long, presumably happy life. You sound like you did your best to make her life good.
It's perfectly normal to grieve and you may have a hard time adjusting to life without your dog, but I don't think your dog would want you to lose your drive.
Think about it the other way, if you were in agony, wouldn't you want it to end? It was your dogs time, its better for your dog to stop being in awful pain and finally rest, rather than have to be alive just your existence. Logically, this was the best thing for your dog. Everyone dies, thats not a bad thing, just life.
Listen I know how painful it is to lose a pet I was told my dog died after school it was horrible she had been with me my whole life. Yes I know it hurts but if you give up on life that will not make her happy it will make her sad. So live your life to full and speak to friends and family, go out and have fun and make yourself happy so she can see you are doing fine without her.
I know that, and that's why I keep moving forward. I'm not here to give up on life, to give up on those who shaped me. I'm not suicidal, but that doesn't take away the fact that the loss I'm dealing with makes me feel indescribable.