Sharing a bed with someone can be one of life's great little pleasures. It's a constant comfort, and reminder of the intimacy and trust you have with another person.
It is also a logistical nightmare.
You've got different sleeping positions, light-level preferences, pillow arrangements—not to mention temperature needs. Thermal distribution in a two-person bed is a study unto itself, in fact. Some people want the room to be ice cold, while they are baked alive beneath a pile of covers. Other people require that a fan blows air across them all night, which they then counter by using an extra blanket. And I'm not calling out anyone, anywhere for being weird—by default I sleep with both feet outside the covers (because, for some reason, bed makes the bottoms of my feet go thermonuclear with heat) and a secondary pillow tucked under my right shoulder, taking a bit of my weight so I can breath easier.
Combining two of these weird sleep combination locks is an interesting process, requiring a lot of real time and dedication.*
*Pro-tip: Develop an automatic "anchor response," where you hold down your side of the covers whenever you feel the other person move.