How are Lia and Cassie connected?

Lia and Cassie are two of life's perennial outcasts. They're going through some major problems in their lives and as a consequence feel disconnected from the world around them. More than anything else, it's this overwhelming sense of isolation from a world they don't understand and which doesn't understand them that joins them together.
In addition, like a depressingly large number of girls their age, they both suffer from eating disorders; Lia is an anorexic, whereas Cassie has bulimia. For both girls, eating disorders are a way for them—one of the few ways available—to feel that they can exert some measure of control over their lives. But this is a mirage. To a large and damaging extent, Lia and Cassie's low self-image has been determined by society's expectations of what's considered the appropriate body-shape for girls of their age, and they've internalized those expectations, with truly disastrous consequences.