Unless and until the employer knows about the problem, the employer will not be in a position to stop the behavior. If they know of the conduct and fail to take action, they may become liable for allowing a hostile workplace or failure to stop sexual harassment. But they can't stop anything if they don't know about the problem.

If he wants the behavior to stop without informing his employer, and getting his employer's help, he can ask her to stop.

If he does not ask her to stop and does not report the problem to his employer, he can expect that the behavior will continue.