My Best Friend's Brother That Never Was

Elips Carlisle has had the same two best friends since she can remember. The only explanation for how lucky she is to have them is that fate had a hand in having both of them becoming her neighbors - Joey and her older sister Mandy moved in on one side, and Nathan moved in on the other side.
Nathan was a year older than the two girls, (yes, Joey is a girl) but two years younger than Mandy, and she had already graduated high school. But age never mattered to the three of them. They did everything together anyway.
One day Elips stumbled across some old letters while they were at Joey's house. She realized that Joey was actually supposed to have a twin brother who died at birth. If Joey knew about it, she never told anyone, and if she didn't know, then that means her parents have been keeping this from her for her whole life.
Elips didn't want to tell Joey about it in fear that there was a reason her parents were keeping it from her, and just decided to pretend nothing ever happened...but she never expected what the consequences of that choice would be.

Or...is it that they aren't really consequences, but fate's way of helping Elips's life down the path it was supposed to take if Joey's twin brother had actually been born - the way things should have been?