Friends Like Us by Lauren Fox

For Willa Jacobs, looking at her best friend Jane is like looking in a mirror on a really good day. Strangers assume they are sisters, and they share everything: an apartment, clothing, and groceries, and the challenge of making rent on part-time jobs. Together they are a fortress of private jokes and shared opinions, with a friendship so close there's hardly room for anyone else. But when Ben, Willa's oldest friend, reappears and falls in love with Jane, Willa wonders: Can she let her two best friends find happiness with each other if it means they leave her behind? Paperback, 2012 Goodreads: 2.90