When women have sex a chemical(oxytocin) is released in their brains that stimulates a strong emotional connection to the man they're having sex with.
Soooo they can't leave their emotions out but they can decide to not be someone's side chick.
This only applies to good sex though. Aint no oxytocin levees getting broke for a 4-inch minute man
Its just like this super senior nikka told me my freshman year of college, "Never give a chick your best dikk unless you want her claiming you, period."