It's a state university, and I said that they had "rules about relationship overnights", not that they were forbidden.

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.