I just discovered that your sim can get married but not move in with their new spouse. After the marriage ceremony, when the moving screen comes up, just click cancel, and the rest of the process proceeds as usual, except no one has to move.
I'm sharing this info because it makes it easier to achieve the "Outlive 5 Spouses" achievement. It's also great if you want to keep playing that sim in your "main" household, along with the rest of that family, but want or need him or her to be married.
Kind of cool!