Leave it to the Italians
Italian researchers have discovered a nerve growth factor, (NGF), which correlates with falling in love.
Is it news to any of us who have been young and in love that requited passion fades within a year? (Or that unrequited or unconsumated desire can last a long time?)
This NCG normalizes within a year of a love relationship. But is it cause or effect? Regardless, it is definitely "chemistry." And real life definitely, inevitably, but sadly, runs counter to this chemical bliss.