" Because what we associate with the idea of love is purely chemical. It can be broken down into scientifically proven phases: it starts with a dose of testosterone and estrogen, what we would think of as ‘lust,’ followed by the goofy ‘lovesick’ phase, which is a combination of adrenaline, dopamine, and a drop in serotonin levels—which, by the way, makes our brains behave exactly like the brains of crack addicts—and ends up, if we make it through phases one and two, with ‘attachment,’ where the body produces oxytocin and vasopressin, which basically make us want to cuddle excessively. It’s science. That’s all. "

― Cynthia Hand , The Last Time We Say Goodbye