Yeah, it sucks. Outlived several dogs and cats by now.. eventually you just have to accept this fact of life that their lifespans ain't so long... Tell you what though, wouldn't trade the time I have spent with my dogs for anything in the world. They've brought so much joy to my life, the least I can do for them is mourn them when they're gone. Totally worth the pain. Focus on the fact that your dog lived a good life, and that you've done everything you can to provide that good life.