In Weatheria, when Nami learn about Luffy's situation, she broke into tear by feeling his pain. She even said this "I have to be able to take my captain to any location he wants to go, no matter where it may be" and "If I let him go, he'll die, and he's stupid, so I have to take care of him." I don't know Oda's true intention but that sound a lot like a confession and a promise to stay by his side forever to me.