What is the relationship between magic and love in The Night Circus?

Magic and love are two of the main themes in The Night Circus. Both pervade the book and both influence and interact with the characters, most particularly Celia and Marco, throughout the story. Having said that, love of a variety of descriptions is present throughout the book: platonic love, love of family, love of the circus, and, fittingly, love of magic.
One cannot miss the similarities between the ways in which love and magic are treated in the text. Magic is something that most people are afraid of and are most particularly afraid to admit the existence of. To admit the existence of magic is to concede that there are strange, perhaps higher, powers in existence over which we cannot exert control and the details of which we can never hope to understand. However, as much as people fear magic, or wish it wasn't real, there is a part of them that needs it to be real. That is why people return to the circus. They need to believe in something wonderful, something beyond the corporeal monotony of this world, something that is mysterious and...well, magical. Without that belief, no matter how tenuous it may be, the world seems very gray and empty.
The same is true of love in the text. For all the complications it brings, both Celia and Marco become aware that love is the singularly best thing about their lives—lives which, without love and magic, would be considerably smaller.