Slut GF’s Surprise Birthday Turn

so, weird uncles birthday party vibes were the last thing on my mind when I got home that night, but honestly, the whole thing ended up feeling way more like a twisted family reunion than any kind of celebration I could’ve imagined, because there I was, thinking I’d surprise my girl with a cake and some sparklers, only to walk into our bedroom and find her bent over our shared mattress with my so-called best friend buried deep inside her from behind, his hands gripping her hips like he owned the place, and she was moaning this low, guttural sound I’d never heard her make for me, her back arched so perfectly that the dim lamplight caught the sweat glistening along her spine, and for a solid ten seconds I just stood there frozen in the doorway, the cardboard box of vanilla frosting digging into my palm, watching the way his balls slapped against her wet folds with every thrust, the rhythm so steady and practiced that it hit me this wasn’t some drunken mistake—they’d done this before, maybe a hundred times, and the smell of sex and cheap perfume hung so thick in the air that I could taste it on my tongue, a mix of her coconut lotion and his musky cologne that made my stomach churn, but I couldn’t look away, couldn’t move, because when she finally turned her head and saw me, her eyes were half-lidded and glassy, and she didn’t scream or push him off—no, she just smirked, reached back to spread her own cheeks wider for him, and whispered, “happy birthday to me,” while he sped up, grunting like an animal, and I stood there realizing the only surprise was how much my heart was pounding not from anger but from the sickest, hottest arousal I’ve ever felt, watching my whole world get rearranged right in front of me.