Please help me to stay on track... (Read if you can)

The main creatures, these Fairies that more or less thrive off of the happiness put off by humans, are gathered into a roving Gypsy band. Most of them are children. They are only as old as the oldest that they have ever acted, so most of them are eternally children. When one of them does something more 'grownup' such as swearing, or kissing, or not using their imagination for any length of time, or pretty much anything that you don't see a five year old doing, they grow up to that age. If they hit a certain age, around 16-18, they usually loose the magic altogether and become human, forgetting the life they lived as fairies. When they do something very mature and selfless, such as jumping into danger to protect someone else, they age VERY quickly, but typically stop at around late 20's to mid 30's. They don't age from there if they keep a childlike mind, but they are much stronger and become the elders of the camp.

The main villain, a being that has yet to be named and likely never will, is a darkness that feeds on misery. It uses contracts to ruin the lives of humans, changing the greatest moments of their past into horrible mistakes or wasted opportunities. It convinces a human at a time of weakness to accept this contract by offering what could, by some, be considered equal trade. In many ways, this is like selling your soul. The being manipulates time, changes the parts of your life that are included in the contract, and then feeds off the mess your life becomes.

The main character is a girl, unnamed at the moment because I happen to know her IRL. I'll think of something for her later. Her original destiny was to fall in love with one of the fairies, and become one of them herself. A contract is offered, however, and that fate is altered forever.

The story starts with the girl at home alone. The fairies, mischievous as they are, want to play with her. So, of course, they knock and then come in uninvited. Still, after a few awkward moments, she learns that they are no danger and befriends them. Returning to the camp of the Gypsys, she meets the fairy she is destined to fall in love with. They are friends immediately, and he visits her often. Eventually, however, her age starts to change the relationship. She is growing up, from 12 years old when she met him to 16, and he is still 14. Her sadness causes him to lose health, and his weakened state introduces despair. This is what first attracted the antagonist, and he offers her a contract. The contract is such that she would never feel this pain again, but the method of stopping this pain is not mentioned. She signs the contract... And time unwinds itself. The fairy is not there when she first visits the camp, and she never meets him. The camp still stops by the town every year, but she sees no reason to visit them. Eventually, however, her dreams begin to show her a life that never was, and she realizes the most horrible mistake she has ever made has not even happened yet. The book ends when she finds the Fairy camp and meets the fairy she fell in love with, and the the truth is revealed that all of this happened during the moment in which she is signing the contract. She scratches the first half of her name off the page and returns to the camp, racing to catch it as it leaves, and joins with the person that matters most with her. The single moment of happiness makes her a part of the camp, and (someone shoot me for saying it...) they live happily ever after.