When you first fall in love, passion naturally rushes through your veins. You can’t get enough of your new partner. But then … you get to know him or her. And as passionate love transitions to companionate love, the passion eventually fades. This is, in part, thanks to the chemistry of love, which involves two phases (in simplified terms): the first, new love, is often marked by spikes in dopamine, serotonin and adrenaline, and the second, attachment love, is facilitated by oxytocin and vasopressin.