Pet or animal companion grief can be a "disenfranchised Grief" a kind of loss that people around you may not understand, or may not respect as a legitimate deep personal loss.

Pet grief can feel incredibly intense for multiple reasons
Pets often share our daily lives and routines in a close way that even our closest humans do not. Maybe you slept, ate, or walked together daily, or they greeted you at the door every single time you walked in.
Our animals may have shared major life stages and milestones with us, and we grieve for the lost times and treasure our memories, for example with the cat or dog we have had since we were little children. Or maybe your pet had been there for you when you were lonely or ill.
Animals can also be accepting of us and nonconditional in a way people usually are not. And in really tough times it may feel that the pet was your only friend or the only one who did not care or judge your imperfections.

You are not alone and I hope you will have special memories of your beloved pet to treasure always.
Take care of yourself.
Sometimes mementos, pictures, going to places where we had good memories can be a part of healing. Find people who do understand how impactful pet loss can be.

Here are a few links to get you started:

https://www.rainbowsbridge.com/grief_...

https://www.agentlerest.com/petloss...

really good song and video about grieving a dog:
https://digitalbeatmag.com/bloodywood...

Helpign Kids cope with pet loss:
https://magazine.vetmed.ucdavis.edu/f...