A shared bedroom teaches negotiations that have no formal minutes.

Sharing a room teaches negotiation before you have any of the vocabulary for it. Light, noise, mess, hours, the invisible line down the middle, all settled by trial and irritation and eventual accommodation. Nothing is written down, nothing is enforceable, and both people learn to concede in ways they will not be able to explain later. It is a genuine education in living with a will that is not yours.

If you shared a room, look at what you learned there that still runs your relationships now, including the concessions you make automatically. Some of them are good and some are just old. Knowing which is which lets you keep the skill and drop the reflex.