Katelyn has sought out the help of a social worker to try and understand why she continues to have poor relationships with others. In gathering information, the social worker discovers that Katelyn has been engaged three times since the age of 19 and just had her 23rd birthday. She has been fired from six different jobs and could not finish college. Katelyn describes her demeanor as being extremely happy or really down in the dumps depending on the situation. The social worker begins therapy for what disorder?