Just saw this thread and thought i would throw in my opinion, after all, that is why I am here.

From my point of view I would agree that the collar is yours, and the only way it belongs to him is if you walk away form the relationship. From your description this is not what happened, so you should have had the choice as to what to do with the collar.

As for the ohter items, that was definately petty, and I would asay that you are probably better offf without him in your life. Take some time and heal, and then go find yourself a new Master that will treat you the way you should be treated.