Forbidden Book by Tabitha Suzuma

Seventeen-year-old Lochan and sixteen-year-old Maya have always felt more like friends than siblings. Together they have stepped in for their alcoholic, wayward mother to take care of their three younger siblings. As de facto parents to the little ones, Lochan and Maya have had to grow up fast. And the stress of their lives—and the way they understand each other so completely—has also brought them closer than two siblings would ordinarily be. So close, in fact, that they have fallen in love. Their clandestine romance quickly blooms into deep, desperate love. They know their relationship is wrong and cannot possibly continue. And yet, they cannot stop what feels so incredibly right. As the novel careens toward an explosive and shocking finale, only one thing is certain: A love this devastating has no happy ending.