The bond you share with Luffy is a collection of mutal understandings and boundaries; you don't expect any more from your captain. It was enough that you two could kiss and cuddle as much as you wanted— it's just a problem that it confuses newer crew members. But it's not really your problem so you continued on with your relationship, one without a label. It doesn't matter to you or to Luffy, most of the crew have gotten used to it at least.