Is there any brain condition that interferes with one's ability to fall in love?

Interesting question. As a psychiatrist, i can't help but feel that brain activity is part of all psychiatric illness. Yet if people can idealize others, they can "fall in love" -- whether it leads to healthy relationships or not. Certainly there are delirious and traumatic brain conditions which so disorganize perceptions and connection with others, that they disturb ability to empathize and relate.
Read the DSM-IV. Unfortunately there is an entire book devoted to disorders of personality, called the diagnostic & statistical manual of mental disorders (currently version 4). You need to see a psychologist or psychiatrist. Your question is too vast for the 400 character answers here on health tap!