Still needs to be discussed beforehand, whether you have partners or not - easy to overlook this because he didn't have one at the time, but gf and bf are pretty much the number one cause of dissolution between flatmates
Ultimately you have to be happy where you're living and giving in to his requests, you might accept at first, but will continue to feel dissonance about it and then end up in the same argument down the track but a harder fight
Get a flatmate who is a hopeless romantic failure - he'll never close and you'll never see more than one shower from him