Myth: X character in One Piece is in love with X other character in One Piece.
Fact: It is not uncommon to see pairings mentioned like Luffy x Nami, Luffy x Boa Hancock, Sanji x Nami, Zoro x Nico Robin, Zoro x Tashigi, Franky x Nico Robin, etc. however some fans try to force the speculation into fact when it is not.
Fans love to fantasize about possible character couples.
When asked if there would be romance in One Piece in a SBS letter, Eiichiro Oda replied “they are in love with adventure”. There are no hints released in the manga itself. There exist minor love stories such as Kyros and Scarlett’s love story and certain relationships have been addressed (such as Piiman, Tamanegi and Ninjin mentioning how Usopp is a “lucky man” to have somebody as Kaya) but they are rather minor and no major relationship has been officially confirmed.
As such, most love referencing comes in the form of perverted comments from one character to the other. Oda said that since this is a shonen manga, there is practically no romance (with a few exceptions, such as married couples, etc.). Not counting Sanji’s feelings towards almost every female being in existence, Oda took eleven years to introduce any form at all – Boa Hancock’s love for Luffy.
However this is considered to be a one-sided romance solely intended for humor as Luffy does not have those same feelings for Hancock, having turned down her marriage proposal several times in the past.
Oda also mentioned in one of the SBS that One piece is manga targeted at young boys, therefore there will be no romance between the Straw Hat crew.