FI and I live relatively near to each other, but if he stays at my house, its understood that we'll have separate rooms. And my mom assumes that if we stay at his house, we'll have separate rooms.
When we went on an overnight trip to the French Quarter with his family for his 21st birthday, my mom assumed it was girls in one room, guys in the other. Right. We stayed in the same bed in the room with his parents. Scandalous.
His parents really don't seem to care all that much, which is good. My mom, on the other hand, cares enough for both of them.