The Brain Chemistry Of Love And Lust
http://www.mcmanweb.com/love_lust.htm
1) Lust (the craving for sexual gratification) is driven by androgens and estrogens.
2) Attraction (or romantic or passionate love, characterized by euphoria when things are going well, terrible mood swings when they’re not, focused attention, obsessive thinking, and intense craving for the individual), driven by high dopamine and norepinephrine levels and low serotonin.
3) Attachment (the sense of calm, peace, and stability one feels with a long-term partner) driven by the hormones oxytocin and vasopressin.