In light of the additional information you have provided, and assuming that the girl is also in love with the boy, the usual ways these stories wind up is either the girl loves the boy so much that he lets him bite her so that she, too can be a vampire, the girl leaves the boy, even though she loves him, the boy tells the girl he is a vampire, but then leaves her for her own good, or they both kill themselves like Romeo and Juliet, choosing death as opposed to living apart.
Ho hum. Been there, done that. Why don't you get really creative and make up a totally different story and ending? I will offer some possibilities, and you can take it from there! Use your imagination and write something really out-of-the-box:
- The girl just so happens to be a chemistry nerd and decides to go to work to find a formula that can turn the boy back into a normal person.
- The girl happens to be a biology nerd and finds a special type of substance that the boy can drink that takes the place of blood - some sort of compound that satisfies his need for blood, without being blood.
- The girl and boy both become astronauts and colonize another planet, where vampirism cannot survive in the planet's atmosphere, and they live happily ever after.
- The girl wakes up and finds it is all a dream and no one is a vampire, neither the boy, her mother, etc.
You get the idea! Good luck.