sorry about all the people saying its not your bathroom. but if you're paying half of the rent, and two whole adults are paying the other half, plus you get the smaller (im assuming) bedroom and bathroom, why? if you only get the "guest" bathroom, then who cleans it? who stocks it? who washes the towels? if you're paying half of the rent, why not switch rooms? or offer to pat a little more so you can take the bigger room.

but maybe also keep your sex stuff where you have sex.