Has it occurred to you that perhaps the BF enjoys the fact that the dog does not respect and obey you? The fact that he undermines your efforts is an indication that he does. This power struggle is a preview of coming attractions. Are you SURE he is worth it?
You might try an umblilical cord for a few days if you are home with the dog. Just tie one end of the leash to your pants and the other end to your collar. Then just go about your daily chores. She'll get the idea you are alpha.