Some doors you have to lock from the inside. Nobody else can do that part for you.

Certain endings only hold because you keep enforcing them. Other people may go on testing an arrangement you have already decided about, and no announcement makes that stop, so the decision has to be maintained by you each time it is questioned rather than settled once by agreement. That is unfair and also how it works.

Decide privately what you are no longer available for, and keep the decision without needing it acknowledged. Expect to hold it again, quietly, several times. You do not need the other person’s cooperation to keep your own side.