So I have realized after pondering last night, that the way Oda has written Luffy. Unless he dies there's no settling down for him... He made him such a dependent child.
If the Strawhats marry and leave.
Either Luffy will be sailing forever, or he lives with someone.
But after two arcs of Luffy forcing Sanji along and not taking no....
If Sanji and Nami get together, Luffy will either be their neighbor or their roommate (adult child.)
If Luffy and Nami (God forbid) got together. Luffy would make Sanji live with them anyway.
I don't know how Oda is going to tackle that.