I know what it feels like to lose pets. I've lost 3 cats, a dog, and a spinifer(scorpion looking spider thingy).
My first cat I called Ina. I only had her for 2.5 years until she was savagely attacked by a raccoon. She used to accompany me to school while I walked, and had never clawed/bitten me ever. In the last moments of our time together, When I was trying to see what had happened, the second I was about to go over the wound, she clawed me for the first time since I got her.
My other cat, Jimmeh(yes, with the eh at the end.) I had for 4 years after ina died. This one was just brutal. He used to climb up trees and kill birds and squirrels. One day he got stuck up in a TALL tree in my backyard, and was too afraid to jump down. A week later, it managed to get down, and I fed him practically everything he wanted. One time he managed to get outside when I was taking the trash out, went missing for 4 weeks and came back completely beaten, bloody, and had lacerations everywhere. He got put to sleep within 4 hours, it was expected he would die by the next day.
My other cat, Stella, I had for half a year, I adopted her, but was never informed she had colon cancer. After I figured it out, she was put to sleep as to not be in pain. I always thought something was wrong because she hated being picked up or having stuff touch her stomach.
My dog, Lessi, she had a heartattack at 2, only had her for about 1 year and a half. She was the best dog I've ever owned. She had a heart disease.
My nameless spinifer, he died after 3 years, considering thats its lifespan.
Good luck dealing with your loss.