Has anyone ever had a feeling of guilt after the death of someone/thing?

My Newfoundland ped on last night at the vets after being bit by a rattlesnake on the head and I keep blaming myself for it. If only I had reacted sooner, if only he was on his leash, if only I had never taken him outside, he would still be alive. I have never felt so ashamed of myself before. What makes it worse, my dad is on his way to pick up his body from the vet so we can bury him in the backyard which means I will always have a constant reminder of him every time i step into the yard, every time I look out my window. I don't know why but I'm afraid. Thoughts? Opinions?