Well, I would think that being in love with someone would mean that you love them for everything they are and do, including their faults. Being in love with the idea of someone would mean you fantasize about the perfect relationship with the perfect person who may or may not exist. ?
Being in love with somebody, is loving somebody for who they are. Accepting their faults and putting them behind you. Being in love with the idea of somebody, is loving what you think they could be, instead of what they are.