He brought up the option of husband and wife in separate bedrooms.
Before we started dating, I'd known my now wife for a couple years and was interested in her. I knew I had an opening when she said that her ideal living situation with her long-distance boyfriend of several years was to have side by side townhouses. Some fast talking later, she breaks up with him and we're still together after 15 years.
I can't honestly imagine having totally separate living space from someone to whom I still wanted to be married. If they bug you that much in close proximity, something's wrong with the relationship. (Separate activity space, "caves", like Void's example? Sure. Bedrooms? No.)
yet people want to change everything about their SOs when living together.
A big reason that many relationships don't work, IMO. You shouldn't expect people to change, or be with someone who expect you to change in fundamental ways.