Biology in romantic love
Dopamine, norepinephrine, and serotonin are more commonly found during the attraction phase of a relationship.

All these chemicals stimulate the brain's pleasure center. But this stage only lasts 1.5 - 3 years [2]. That's why 'we no longer feel the initial feelings of love'.

Oxytocin and vasopressin seemed to be more closely linked to long term bonding and relationships characterized by strong attachments [1].

Attachment makes relationships last for years and decades. It is based on commitment and mutual friendship. Oxytocin and vasopressin are at higher levels [2].

The neurological process involved in the perception of heartache is not known, but is thought to involve the anterior cingulate cortex of the brain, which during stress may overstimulate the vagus nerve causing pain, nausea or muscle tightness in the chest [3].


Image from Wikipedia [1]

References:


Wikipedia contributors, "Biological basis of love," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Biological_basis_of_love&amp;oldid=613867553 (accessed June 26, 2014).
Wikipedia contributors, "Love," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Love&amp;oldid=614240299 (accessed June 26, 2014).
Wikipedia contributors, "Broken heart," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Broken_heart&amp;oldid=613979584 (accessed June 26, 2014).