As an 'One Piece' diehard, I can tell you that Monkey D. Luffy doesn't show any romantic interest in anyone. Eichiiro Oda, the manga's creator, once stated that there wouldn't be any romance among the Straw Hat crew. Luffy's obsession is primarily on adventures, his crew, and his pursuit of becoming the Pirate King. Love in a romantic sense doesn't really factor into his narrative.
Still, you could argue that he deeply loves his crew members and his allies, albeit in a familial or platonic sense. His dream and his camaraderie define him, not a romantic relationship.