I too am pretty sure cats grieve. When my Zsa-Zsa's brother Brando passed away, she wouldn't eat, so she lost a ton of weight, and she would cry for him, literally cry, she would sit infront of his basket and wail with her eyes streaming kitty tears. Shortly after that, she went blind. Whether that was anything to do with Brando's death, or the crying, we'll never know, but it seems a very big coincidence. To help Zsa-Zsa get through, I just gave her as much love as I could. I know she still misses Brando but she is now a very happy cat. I'm so sorry that you have lost some of you cats.