I totally understand about the dog, too.
My ex got a puppy in Spring of this year, only because I encouraged him to go look at them (black lab pups)...he fell in love with one of them, and he technically got it (but I love the dog, too!). And he has always said he wouldn't have him if I hadn't told him to go looking.
Then over the summer, I got a mix pup...and these two dogs became best friends, plalyed all the time together, slept by each other, everything.
My dog seems to be just as sad as I am now that my x (and his dog) are gone.
They are part of the family, too.