Writing a history of events accounting occasions when someone(s) breaks the mutually established boundaries and expectations is a first action to take in asserting and advocating for oneself. Sharing those events with the someone(s) who broke the boundaries and expectations would be the second action. How they receive and respond to the revelation of their honest or malicious mistake will determine how to proceed with advocating for yourself in the relationship.
Hopefully the offending party is a positive, healthy, expansive person(s) who will receive and respond to their mistake in a positive, healthy, expansive way. We all make mistakes from time to time.
Fortunately, in a positive, healthy, expansive relationship both parties benefit when they share and receive with each other a perceived mistake. By sharing and receiving crossed, as well as met and acknowledged, boundaries and expectations a mutual respect may continue to be cultivated.
Unfortunately, the offending party may not be a positive, healthy, expansive person(s). Even worse, if the negative, unhealthy, contractive party is also in a position of authority. How would one respond?
Fortunately, we live in a society with some checks and balances. There are parallel and higher levels of authority to respond to parties in authority who break boundaries and expectations.