From the little information you have given us, it seems the fault lays on your boyfriend's shoulders, and yours in that the dog needs training. Just like you'd train a puppy, this dog seems to not understand the "rules" of living with people. Enroll in an obedience class with him, and see how that goes. Just because a dog is 5 years old doesn't mean it has had any kind of training, and an untrained dog is a danger to others and himself.