I had to take my partners cat to the vet to be put to sleep while he was working abroad. It was heartbreaking for us both. He had him for six years before we moved in together so was always really "his" cat. I know it wasn't my fault (poor boy deteriorated VERY quickly completely out of the blue and it turned out he had a blood clot) but I feel horrendously guilty over a year later for what happened and that I had to do it while OH wasn't here to say goodbye. It's a horrible feeling to have to make that decision but I know at least I was here for those final moments, stroking our boys paw and telling him his dad loved him so much.
Poor Bonnie not having her humans there with her in her final moments. So sad.