I read this book a few years back, can't recall the title, but the girl has some form of terminal illness - I think it's a blood disorder - and she falls in love with the guy who lives next door to her. The book's in first person, and at the end, she dies, and throughout it, it has these letters written to her by the people who love her. If anyone can let me know the title and author of this, I'd really appreciate it. 
Thanks!
Thanks!