Liz,
The best thing my XAH did was change the passwords, facebook, email and phone. I didn't feel that at the time, but me monitoring everything kept me in the hole. So the less i knew the better.
I get it about the dog. My X as taken the dog multiple times since our divorce in October. He really does miss her. No kids at home and no dog. Even on Valentines the X sent me a text that said "Happy Valentines day. Its lonely with no one and no dog."
So I do get it, He made his bed and he has to lay in it. I would be devastated to have to give up my dog. So try and find a little compassion as it is hard for even the A. Sorry not what you want to hear, but its probably good for the dog to see his daddy also.!!