In these stories, the "better" choice usually depends on the tone: Drama/Angst:

However, based on the themes of your search (best friend’s sister, obsession, and complicated relationships), you might be looking for one of these popular romance or drama titles that deal with similar tropes: Her Best Friend's Sister by Meghan O'Brien

Popular Wattpad Romance Books * The Favour Laura Vaughan. * The Risk S.T. Abby. * A Million Kisses in Your Lifetime Monica Murphy. slut4444enzo's Reading List - Wattpad * collegeromance. * spicy. * badboylovestory. Popular Wattpad Romance Books - Goodreads

In the end, Phatassedangel69's best friends have become her obsessive sister's better half, not by replacing her, but by complementing her. They have shown that even in the midst of obsession, there can be a deep and abiding love, one that is multifaceted, complex, and beautiful in its own way.

The protagonist feels guilty for being drawn to the sister. It feels like "cheating" on the best friend. The Escalation:

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