The sun was dipping low, turning everything golden. I’m Sam, and this double date with my best friend Kimberly was already buzzing with that tipsy, flirty energy we all loved. Jake, my boyfriend, had his hand high on my thigh. Ethan had Kim half in his lap, kissing her neck while she giggled. We’d been joking about swapping for months—drunk confessions, teasing texts—but tonight it felt real.

Kim locked eyes with me, biting her lip. “We’ve talked about this,” she said, voice ...