Who owns the dog me or my ex-boyfriend?

In December 2009, my boyfriend of over 3 years was again working double shifts and working on christmas day.. My daughter was going away to be with her father for 2 weeks over christmas as I was on work holidays I was feeling very lonely. So this one december day I walked into a pet store and saw the most adorable pup, I asked to hold her and I was in love straight away. Now I am by no means an animal lover, I rarely pat other peoples pets. I paid good money to the pet store for the pup that day and took her home. My boyfriend was very unhappy about it as he had a cat that I am allergic to, and the cat was still living in another home, and he had wanted to move the cat into our place. So the pup put a stop to the cat..Oops lol! I absolutely treasured my new pup. My boyfriend did not do anything for the pup, no toilet training, no walks, hardly a cuddle. My child having no other siblings was now overjoyed with companionship. Throughout the year the dog cost me so so much more money than I realized probably around another $2000 for all the tablets and dog accessories and when she got a tick, she was paralyzed and spent 6 nights in the vet and nearly died. The bill was over $800. I paid for everything. About 2 months later my boyfriend and I were going through a real rough stage and on one emotional day I moved out with my daughter, but was forced to leave the dog behind due to my new place not allowing pets she was now 1 year old. We didn't break up, I just needed some head space from all the fighting. 5 months on (which is now) he has fallin in love with the dog as the two of them have been alone together so much. We just broke up on the weekend, so I took my dog with my other possessions that were at his place. Now I am being accused of stealing his dog, his companion, and I am being labelled nasty and spiteful. This is the only animal I have ever been connected to, I paid for all the food whilst she was still living with him. My name is on all the paperwork for her. Yet my now ex boyfriends mother has rang me and told me I'm in the wrong, I left her behind and now I am not entitled to her. She has offered me $500 to buy her back so I could buy another pup and I said no I don't want another dog. Please tell me, am I a bad person for taking my dog, or is she no longer mine??