When we fall in love, our brains are flooded with something called Phenylethylamine. It’s a stimulant that can be found in chocolate, and like the effects of chocolate on the mood, it doesn’t last. but For the lucky few, even as the human body builds up a tolerance to the “love” drug, other chemicals - like Endorphins - rush in. Endorphins are what flood the brain when long-term lovers touch. They’re what gives them that secure, comfortable, old-shoe feeling. But to keep things from getting TOO comfortable - and keep them exciting - a healthy dose of naturally occuring Oxytocin gets released too, increasing desire.