This may be why any kind of rejection (not just break up rejection) or perceived rejection is so very painful, "Our brains appear to process relationship breakups similarly to physical pain. There may be an evolutionary reason for this. The function of pain is to alert the person to physical danger or harm so she can take protective action. In the animal kingdom, one's chances of avoiding predators are much higher as part of a group than alone, therefore social rejection may have been an actual threat to physical survival for our early ancestors. If this is the case, it might partially explain how difficult it is for many people to let go of the ex-partner and move on."
The Neuroscience of Relationship Breakups
Is the Pain All in the Brain?
Published on April 17, 2011
Evelyn Schmechtig -Cochran