Sanji///Nami is definitely not popular, except among a loud minority and makes absolutely no sense whatsoever. He treats Nami like complete garbage, sexualky harasses her routinely, has spied on her while shes been bathing multiple times including in the last arc, and has groped her. She flat out called him the least trustworthy member of the crew.
Luffy and Nami's relationship is built on respect and mutual trust. They make each other better. Nami will always be the most important woman in Luffy's life, Luffy the most important man in hers. They only make sense with each other.