If you treat students like children, it's not surprising if they try to game the system
At my (secular) university, we did have a few single-sex dorms (optional for people who were uncomfortable with a mixed-sex dorm), but all others were co-ed, though some were separated into all-male and all-female hallways where they'd share a single-sex bathroom.
IIRC even the female-only dorms had no rules about overnight stays (though males had to be escorted around the building by their female host). A university not allowing people to stay overnight reeks of puritanical values.
Regardless, this isn't Victorian England. Men and women mix and live in shared spaces. There are plenty of adult living spaces in the world where people have their own apartment/room, but share bathroom space. That's also common in lower end hotels/hostels for travelers. Requiring that college students live in gender-separated living situations is a bad way to prepare them for the real world.
So you need to have respect for your dorm mate, and your suite mates. And you know that, unfortunately, while "be respectful and adult" should be the expectation, there's always someone that ruins that, and the next thing the college has to set rules and say "this is why you can't have nice things".
And I expect there's a bit of liability minimization on the college's part - I'm not saying I agree, but the college probably has concerns of "it's mid term, and an allegation of inappropriate behavior happens, what do you do?" (and I think there's multiple issues with that, like it's not like that can't happen in same sex dorms, but I'm just trying to think about why the college might see it that way).
I get it - and at my stepdaughter's school there are co-ed dorms of different styles. But what they don't offer, and in this case is what the students hoped to achieve was "give us our own dorm with one bed", effectively.
The issue then also comes down to "well, college relationships aren't always the most durable things" - what happens when they break up? Who has to move out? It's not one person's space. Now the college is also on the hook for ensuring that there's sufficient vacancy (wasted) to handle these situations in other dorms.
Essentially it's one night a week. So, if both students, effectively two nights a week.
I don't disagree. I think it would be disrespectful to your dorm mate if your partner was just living in that space (which is already small for two, let alone three) most of the time. And you have to imagine that's at least part of the reason why such things are rules now, not suggestions.