I completely agree with every response on this thread and I too really struggled when I lost my best friend at age 7 a few years back (she was 7, not me!).
That being said, I know I risk a huge backlash here, but I feel the need to say it nonetheless...
We do awful, horrendous, torturous things to animals by the many billions every year. I strongly believe all of us here feel different to the loss of an animal than we would an inanimate object. Why? Because we are able to build a stronger relationship with a living thing. Because we share so much with them - love, comradery, a whole range of emotions. We both recognise in them and share our sentience. Who wouldn't do anything to protect their animals, to give them the best in life, and - in the event of illness or death - to make it as painless as possible?
While these feelings of grief resonate strongly with us all as we think back to animals we've lost, how can we not recognise that that same respect and love should extent to all animals, all of whom have the same capacities for feeling as those we love and have loved? Knowing their characters and their experiences, both pleasurable and painful, imagine them out in the world if they had not come into your lives and been cared for. Imagine what they would have gone through. The suffering. The loss. The pain. The fear. Why do we value their well-being above other animals whose capacity to suffer is the same, but who have not been lucky enough to find a happy home with us, and all that comes with it?
The dog I had who died at 7 was a rescue. The effects of the trauma of her early life were obvious to see. At the same time there were other behaviours that many dogs exhibit, rescue or not. The upcoming annual fireworks are a common bad time. My dog would be petrified. At the time, I didn't give much concern to animals outside of my sphere. Through witnessing her capacity to experience fear (at this time and many others in her short life), and wanting to do anything I could do to lessen it, the light bulb moment lit up for me that all animals will feel the same, and worse.
To the OP especially, but to anyone else reading this, I am not trying to undermine the feelings of loss. On the contrary. I am trying to amplify them and utilise those feelings in the hope that they can be used to extend out from the personal to the universal.