Put down my 16 year old chihuahua today, it hurts so much more than I thought

My parents got him for me when I first moved out. He was my best friend and companion my entire adult life. Never had many people to talk to and don’t really have anyone to talk to right now… he was my entire world.
He was having so many problems in his old age but was still able to eat and mostly get around, it was such a hard decision to make. But he was getting so hard and expensive to care for, and after a breathing issue last weekend where I thought I was going to lose him, I made the decision to let him go peacefully by my side with an at home visit. But I still feel terrible that he maybe could lived longer…
I brought him to my parent’s and we buried him. And I’m staying with them for tonight. But my niece is here so I have to just put on a strong face and not talk about it.
I got to stay with him all yesterday, feed him all his favorite terrible foods, but I’m already feeling broken just wanting to hug and cuddle him again.
We had several dogs as I grew up as a kid, but Cid was just so special and I feel like there’s a hole I’ll never fill again.