First, a little backstory...My mother got this dog for my grandfather about 7 years ago as a puppy. I've lived with this dog for 5 of the 7 years we had her. I can't honestly say I LOVED this dog, in fact she pissed me off a lot of times, and he often seemed to care more about this dog than he cared about me. I didn't HATE the dog, I liked her, especially as she got older, stopped being destructive and was less of a pain in the ass to deal with...Still, when I heard she was being put to sleep...I dunno...I just feel empty all of a sudden...Why do I feel grief for an animal I didn't care all that much for? Maybe I loved her more than I thought I did? Is that possible? Maybe I feel sympathy pain? I'm confused and tired and depressed...
* I think we grow to love the "personalities" we live with, even if we don't alway "appreciate" them all the time. So yes, I think you probably loved her more than you realized. Losing people/pets creates a change and leaves an empty spot for some time. Give yourself a while to process this loss and change.