The Sky is Everywhere by Jandy Nelson

Seventeen-year-old Lennie Walker spends her time tucked safely and happily in the shadow of her fiery older sister, Bailey. But when Bailey dies abruptly, Lennie is catapulted to centre stage of her own life - and, despite her nonexistent history with boys, suddenly finds herself struggling to balance two. Toby was Bailey’s boyfriend; his grief mirrors Lennie’s own. Joe is the new boy in town, with a nearly magical grin. One boy takes Lennie out of her sorrow, the other comforts her in it. But the two can’t collide without Lennie’s world exploding...