A girl likes a boy in the film, probably a celebrity who doesn't even know her. However, she still dreams of being with him. Since he doesn't even know her, the girl thinks it's fine because she's happy to be by herself anyway. She doesn't really need a boyfriend or something. At the same time, she still dreams on no matter what happens.
This song describe those who are fans of celebritiy or those who like / love someone who doesn't even know them and probably will not even meet them again. However, they still dream to be with that person. In reality / their current real life, they don't really need to have a relationship / boy / girlfriend anyway. However, they still dream on. They have dreams in life and that makes their life richer & meaningful.
(I'm like one of them too! I like this song, even though just I heard it an hour ago.)