One of Luffy's traits is getting people to love him. That's why almost everyone who come in contact with him find themselves either loving him, caring for him, or simply taking his side. That includes men and women, even former enemies.
However, you asked who is genuinely in love with him. I've fallen in love a few times in my life, both with real people and characters, and the common denominator is that I dream of them, fantasize on them, think of them, want to do everything I can for them. My experiences are exactly like Boa Hancock's and even worse. So she's the only one in love with him, the rest love him. Some very dearly.
Nami is not in love with him, but she loves him dearly, and he is the only one she truly trusts. She even suffers harrassments from others in the crew just because with him, she feels safest.