How do you know this? You seem to be basing this on the fact that animals can't speak to us in a way we can understand. That doesn't mean they don't have complex though processes.
You should come to my place and watch our cat Crackerjack interact with our cat Merlin. Merlin is the second newest cat we got and Crackerjack HATES him. None of the other cats have any issues with him, so it's not that she senses something inherently wrong with him, i.e. an illness. She just hates him. She doesn't hate any of the other cats, including the newest cat Minou. Crackerjack was the first cat we got, and over the years we added 9 other cats (we're down to 6 now) and she NEVER acted this way towards any of them. What biological advantage would stalking and attacking him have to her? They eat in separate rooms as they are on different food, so it's not that. She is clearly the alpha cat and the others know it, so no reason to keep beating it in to him. Minou actualy challenges her way more than Merlin does, so why is she not attacking her?
And going back to my Tonks & Rye story - why did Tonks mourn for Rye if she didn't love him? She didn't mourn when our cat Artemis died and she got on quite well with him. What biological advantage would mourning the loss of Rye have to her?