Worst day ever

Right now, I'm pretty much destroyed. I have an old dog who is 15 years old, and have prepared myself for her death. I never, never expected that my beloved Yoda would be the one to die. He's only 6 years old and just Saturday, went on a quick trip with us to Nashville. Yesterday, he couldn't pee. He would try and try and nothing would come out. He also screamed a couple of times and once acted like he was having a seizure. He had a grooming appt today at the vet, so I asked them to look at him. When I came to pick him up, the vet said his prostate was huge, and since he's a neutered dog, it was almost certainly cancer. Xrays showed the tell-tell signs. This is a very aggresive cancer, and by the time the symptoms show up, it has almost always metastisized. The vet said the stuff yesterday may have been from pain, or it was in his brain. It was the saddest thing I've been through outside of my Grandmothers death. My husband, the vet, and I were all crying over his lifeless body. I am inconsolable. I don't know how this hole in my heart will ever be filled up. I'm not a big dog person. I like cats, but this goofy, sweet dog had my heart wrapped around his paw and I don't think I'll ever stop crying.