Helen Fisher in Nautilus:
George Bernard Shaw knew the power of romantic love and attachment. Both, I will maintain, are addictions—wonderful addictions when the relationship is going well; horribly negative addictions when the partnership breaks down. Moreover, these love addictions evolved a long time ago, as Lucy and her relatives and friends roamed the grass of east Africa some 3.2 million years ago.
Take romantic love. Even a happy lover shows all of the characteristics of an addict. Foremost, besotted men and women crave emotional and physical union with their beloved. This craving is a central component of all addictions. Lovers also feel a rush of exhilaration when thinking about him or her, a form of “intoxication.” As their obsession builds, the lover seeks to interact with the beloved more and more, known in addiction literature as “intensification.” They also think obsessively about their beloved, a form of intrusive thinking fundamental to drug dependence. Lovers also distort reality, change their priorities and daily habits to accommodate the beloved, and often do inappropriate, dangerous, or extreme things to remain in contact with or impress this special other.
Even one’s personality can change, known as “affect disturbance.” Indeed, many smitten humans are willing to sacrifice for their sweetheart, even die for him or her. And like addicts who suffer when they can’t get their drug, the lover suffers when apart from the beloved—“separation anxiety.”
Trouble really starts, however, when a lover is rejected. Most abandoned men and women experience the common signs of drug withdrawal, including protest, crying spells, lethargy, anxiety, sleep disturbances (sleeping way too much or way too little), loss of appetite or binge eating, irritability, and chronic loneliness.
Lovers also relapse the way addicts do. Long after the relationship is over, events, people, places, songs, or other external cues associated with the abandoning partner can trigger memories. This sparks a new round of craving, intrusive thinking, compulsive calling, writing, or showing up—all in hopes of rekindling the romance. Because romantic love is regularly associated with a suite of traits linked with all addictions, several psychologists have come to believe that romantic love can potentially become an addiction.
More here.