If there is a relationship that needs to happen eos, it's SanjixNami. It would be their happy ending.
Nami likes someone to protect her and lavish her like a princess, while Sanji likes to spoil, serve and be a knight/prince in shining armor for a queen/princess, so these two are practically made for each other personality wise.
Sanji and Nami will end up like Reylaigh and Shaqqy. There will not be a marriage between them, but they will follow each other to wherever the wind takes them, a romance/marriage the pirate way.