How We Fall by Kate Brauning

Ever since Jackie moved to her uncle's sleepy farming town, she's been flirting way too much--and with her own cousin, Marcus.

Her friendship with him has turned into something she can't control, and he's the reason Jackie lost track of her best friend, Ellie, who left for...no one knows where. Now Ellie has been missing for months, and the police, fearing the worst, are searching for her body. Swamped with guilt and the knowledge that acting on her love for Marcus would tear their families apart, Jackie pushes her cousin away. The plan is to fall out of love, and, just as she hoped he would, Marcus falls for the new girl in town. But something isn't right about this stranger, and Jackie's suspicions about the new girl's secrets only drive the wedge deeper between Jackie and Marcus--and deepens Jackie's despair.

Then Marcus is forced to pay the price for someone else's lies as the mystery around Ellie's disappearance starts to become horribly clear. Jackie has to face terrible choices. Can she leave her first love behind, and can she go on living with the fact that she failed her best friend?