In today's world, sex exchanges for sex and commitment for commitment—never one for the other. For women wanting monogamy, "no sex before monogamy" works because sex becomes intrinsic to commitment. Once sex happens, both parties risk the other deciding it was a mistake and exiting. That's the gamble of modern dating without hard-monogamy marriage structures. Chemistry gets tested in the physical realm; sometimes you discover it's just not there, even after commitment-level escalation.