Worst new years of my life

June of last year I rescued a beautiful Golden retriever who I named Sampson. Sampson was my baby. We went to the offleash park everyday, he loved car rides, he slept in my room he cuddled and played with me, he was my best friend. He also had a grade 5 heart murmur which is pretty serious, the worst grade it can be is a grade 6. Sam was doing great, his heart never bothered him.
On December 23 Sam began having bad diareah with blood in it, so I took him to the vet where they told me his had giardia.. no biggie it's fixable right? I never would have thought what would happen next.
After a few days of treating Sam for giardia we noticed his breathing had become laboured and every breath he took seemed to be difficult for him. So on December 30 we took him t othe vet where they told us he had some sort of infection, ulsers in his stomache and some fluid in his lungs. Me and my mom made sure to elaborate that this had absolutely nothing to do with his heart.. we asked the vet over and over again.. he reassured us over and over again that it had nothing t odo with his heart, so they gave him a shot to "drain the fluid" some medicine for his "ulsers and infection" the day seemed to go a little bit better, his breathing wasn't quite as bad, until right before he went to bed, it began to get worse again. For whatever reason Sam decided to go get a drink of water from his bowl, which is very odd because during the winter he doens't drink from his bowl he eats the snow outside. So i heard him drink and drink until I heard him vomit. I got up to look and saw he had thrown up all the water had had drank and some blood. I began to worry more and more. My mom stayed up with him during the night until about 5 when he began having open mouth breathing, I had gotten up to take some t3s because i just got my wisdom teeth out to hear my mom on the phone with the emergency vet clinic. My mom had called because Sam went outside and just layed in the snow. I went with my mom to make sure I got to say good bye. I knew he didn't have very long. We got in the car and I listened to him breathing and then began the extremely disturbing sounds he made as the oxygen left his lungs. Within a couple minutes of being in the car, Sam layed down for one last time and then he was gone. I started crying excessively. I couldn't believe it. A year and a half wasn't long enough. We got to the vet and had to take Sam out of the car. i began to lift him, but couldn't hold on because all the blood/fluid in his lungs began to poor out. The nurse who was very sweet took him into the other room and we got to say our goodbyes and then we left him there.
The vet nurse was sure to warn us to stop using out vet for our other dog Kirby, she says that they've seen lots of his patients and he wasn't good. I want to scream at him, I want him to feel that hurting i felt. He assured us it had nothing to do with his heart, he would be fine.. he wasn't. Instead I had to see my dog die in my own arms and I have to have this new year begin without my best friend.