This is from a Ray Kurzweil book, in case anyone wanted the source. How to Create a Mind: The Secret of Human Thought Revealed is the title.

This is actually a really interesting topic, considering the neocortex is typically associated with higher functions like consciousness, language understanding and production, cognition, abstraction, problem solving, motor and sensory integration, etc. Normally, emotional things like love and empathy will be associated with the limbic regions, which are really considered the 'emotional core' of the brain.

However, since we as people have to evaluate others' behavior (body language, behavioral patterns, general emotional signals, etc.) so often, emotions really begin in the parts of our brains responsible for logical analysis. After we process the data, it becomes closer to love.

As far as his idea that you lose a part of yourself when a loved one leaves, it's not wholly understood why we get sad; his idea is just one of theories. Some more, relatively easy reading if you're interested here