Emma and Josh are best friends that grew up as neighbors. They would always run back and fourth to each others houses and do things ordinary kids would do such as, going outside, play together, chill out. As they got older, something awkward happened between them during the summer that caused a bit of distance between them. But things start to change once they get into something and they are back to being back and fourth.
The plot of The Future of Us I believe is how Emma tries to avoid the things on facebook about her future. I know this because in the book there's a part where on facebook it says she cooked mac and cheese for dinner but the next day or later that day when she went back on it had said she cooked something different from when she checked the following time. Also, she's starting to wanna change things around because she isn't loving the future she's reading about.
