I have felt something akin to your pain. We had the "smartest cat ever" - he was like a little person, and just so friendly and adventurous. We are quite sure a certain person across the street poisoned him. One morning he started throwing up. We watched him dying at the vet, and then got him "the shot" and watched his body as life left him. I grieved for him as I would for anyone else I loved. We were able to move out of the neighborhood, thank goodness.