Many people have had a cohabitation situation where sleep schedules don't match up and it can lead to a realtionship-based power struggle. Now, let's factor in romantic relationships. When you share a space, but not a schedule with a romantic partner, it can get tricky and sometimes contentious. With this one, I promise, it's more complicated than you think and not what you were expecting.
Me and my BF moved in together a few months ago. Our apartment is one bedroom and we have a couch. I set an alarm for 6.30 so I can try go for a run with my friends. It's not possible for us to do this another time, unless it's at night.
BF's job doesn't have standard hours, right now he has 2 days each classified as morning, afternoon and overnight shifts, and day 7 is off. My alarm doesn't usually clash with anything because he's either already up or at work by then.