"First, Bullying doesn't end until the person bullied ends it. Period. "

This simply isn't true.

You can stop bullying of a third party by making it impossible (ending any access to the victim [think 'restraining order' or 'moving to another state']) or by changing the risk/reward calculation (e.g., through constant direct supervision by a person empowered to severely punish offenses).

If it weren't possible for a third party to intervene, then disabled people, babies, and frail elderly people would be endlessly bullied by (some) caretakers, and if your family moved halfway across the world, then the bully would be required to follow you, because you didn't "end it".

Note that the bully will still be a bully: your assertion is solely about whether a given individual person is required to remain a victim unless the specific individual decides to take direct action to change his victim status.