Literally every freshman dorm in the US has this arrangement, not uncommon, not bizarre, it's even considered part of the "college experience."
You do that in situations where that's all you can afford, like when you are a student.
My sister spent a year with a volunteer organization in her mid 20s, their living stipend was very small, so everyone lived "group home style" with 2 to a bedroom. In her house they even had someone sleeping in the landing area at the top of the stairs. They actually rented a fancy luxury apartment but ended up being cheap because the rent was split seven ways.
I've maintained a relationship during the time both myself and my partner lived in dorms, you (tactfully) make arrangements with your roommate and work around each other's schedules. You've never heard of a doorsock? We didn't use a doorsock, we duct taped the door locked if there was even a chance of a roommate coming home so they didn't walk in on us.
I believe most dorm rooms are like this for first year students across the US. Where I went to college, it was 2 to a room but some opted for privates. It was kind of odd to do a private suite - living with someone in a dorm room is part of th first year college experience, at least in the US.
I've heard of people who go on to share their room later in college and even into adult life. You do what you have to do. Almost all those cases are temporary anyways.
It's extremely normal for students living in dorms (and frats) in the US--especially for the first couple of years of undergrad. (It's certainly less common--though hardly unheard of--for grad students.)
Maybe your partner has a single room. Or, as others have mentioned, you make arrangements with roommates to stay out of the room for a bit--and maybe someone stays quietly overnight and the roommate tactfully avoids paying attention.
Trust me. Roommates are very common in US undergrad housing and students manage to indulge in, um, romantic behavior just fine. If there's a willing participant of the opposite (or same) sex, life will find a way.
I didn't want (and didn't have) even housemates after school. Maybe it's a cultural thing (don't really know the norms in other countries, see you went to school in the UK), but having roommates through at least part of your time at US residential colleges is almost obligatory. And, as others have noted, it's often seen as part of the experience of transitioning to college.
When I was a student I shared a two bedroom apartment with three other guys- two per room.