I promise most of my posts won't be this sad.
One of the things you may not be prepared for when you get involved with a rescue or shelter is the grief you feel when an animal dies. Animals will die, no matter what you do or how well you take care of them. They may come to you old or ill. They may come to you healthy and then get sick. You may struggle to keep an orphaned young animal alive, only to have it slip away. The point is, you will experience death and grief. Eventually you develop "professional numbness" - which means the death of an animal is sad, but you don't go through a grieving process.
Please don't be dissuaded from getting involved with an animal welfare organization because of this. There are many more good, joyous, magical times than bad, but this is one of the bad things that goes with the territory.
I recently had to put down an old dog who had lived with me for about three years after being brought to the shelter as a stray. "Professional numbness" didn't save me. I went through the whole painful grieving process, including anger. I was angry at the last vet who saw my old boy, for not being able to improve his quality of life. I was angry at his former owners for casting him out when he got to be too much trouble.
Anger is poison. You need to get rid of it somehow. I couldn't stay angry at the vet. I know as well as anyone else does that sometimes there's nothing you can do. I ended up writing an open letter to the dogs former owners and posting it on our shelter facebook page. In retrospect, not only was it therapeutic for me, but it was good exposure for our page. There were many supportive responses and shares.
Here is the post