Honestly, dark(ish)/obsessive Nami is an interesting concept to me. Oda memes on her and Zeus' relationship a lot (well, to be fair, he kind of memes on Nami in general) - but try to remove all those comedic elements, just for a little bit. She's so genuinely warm with women, makes friends so effortlessly. I always think about what she said about Tashigi here:

And she just strikes me as someone who'd go for a girlfriend who's a little older, unintentionally. Just think about it - first she was an orphan, then Bell-mère took her and Nojiko in and they didn't exactly have an easy life - until all of that got absolutely destroyed by Arlong. She never had it easy and it all just got... worse, actually, until she joined the Straw Hats. So, we know this. And we've seen how much she bares herself to the various girls and women of the story - Vivi, Lola, Shirahoshi, Wanda (and, of course, Robin)... I think someone who's not as aloof as Robin, who is warm and oozes comfort, who lets her in and lets her be herself, in all her entirety - that's someone she'd fall for. A sprinkle of mommy issues, a pinch of traumatizing childhood and you have the perfect requirements for a partner who can get weirdly clingy, quickly dependent. And if you let her 'run free' with her little gang of rascals, just provide a safe base to come back home to, unwavering affection and love - she'll never want to say goodbye. She might not realize it herself, but she needs that stability. Comfort. Warmth. It won't take her long to feel like she can't go on without you, without the way you make her feel. Sure, her feelings for the Straw Hats are grand, but you... you're just a touch... closer to her, feed that need to be loved and cherished a little better, a bit more intimately. Nami doesn't look the part, but I think she'd be fiercely protective over you and she's incredibly scared of losing you, ultimately. To you, she's probably nothing but gentle, almost pouty when you're saying goodbye for whatever reason, but to others, she's so different. That calculating, knife-sharp girl, who knows how to use everything she has to get an advantage.