Do you remember in your early relationship with your lovers/spouses, how your hearts raced when you suddenly heard their voices on the phone. How you had butterflies in your stomachs when you prepared to meet them?
Lust evolved to get you out looking (associated primarily with estrogen and androgens).
Attraction evolved to make you focus and expend your energy on one specific individual (associated with elation and craving for emotional union linked to likes of serotonin).
Attachment evolved so you would stay with that individual and raise offspring once mating was accomplished.
Well, something new to learn.
** Inspired by John J Ratey