It's hard when you adopt a little kitten that looks the picture of health and is full of energy--then begins a downward spiral so quickly, all the while you're trying to do everything you can to keep them healthy.
It is the cycle of life, I suppose, and gratefully wasn't a child. But our hearts have lots of room for love--and consequently--for pain. This pain in not as heart-wrenching as that of losing a loved family member, though some people count their pets as family. But, we are continuing to work to keep his sister from falling to the same fate. She seems more robust--though that didn't seem to be the case at the beginning.
Now, I'm hurting because my daughter, Sarah, is hurting, and because I loved the little kitty myself. She loves her little cats, and has wanted her own cat(s)--again--after having lost other cats/kittens due to health issues, as well, or because they simply got lost in the past.
Life--including death--continually challenges us. Hopefully, we'll grow and be better for the experiences. But right now, we're sad.