People with borderline personality disorder often feel intense anxiety about being separated or abandoned from the people they care about. They may prefer not to be alone and come across as “needy” or demanding in the time, communication, and attention they seek from their spouse, family, or friends. They might go to extreme lengths, such as stalking a person by tracking their phone or following them. Indeed, research suggests that 45 percent of people who engage in stalking behavior may have borderline personality disorder.